## 1. Varieties of Modality and the Target of the Epistemology of Modality



The broad focus of the epistemology of modality is the so-called
"alethic" or "objective" modalities. These are
usually identified with those modalities that respect the T axiom of
modal logic, \(\Box p \rightarrow p\) (if a proposition is necessary,
then it is true, where the box stands for necessity). Non-alethic
modalities, such as deontic modality (which has to do with obligations
and permissions, namely what is *obligatory for one to do* and
what one *is permitted to do*, according to, e.g., the moral
norms, or the law), do not obey the T axiom, since, e.g., even if one
is obligated to do \(p\), they might not do \(p\). Although epistemic
modalities do respect the T axiom (if one knows that \(p\), then \(p\)
is true) they are usually ruled out "by hand", so to
speak, *qua* non-alethic and non-objective, since they are
thought to be dependent on the epistemic subject.



Among the alethic (or objective) modalities we find logical, physical,
and metaphysical modality. Where \(p\) is a proposition,
*logical* and *physical* modality are standardly defined
as follows:


* \(p\) is *logically possible* iff \(p\) is consistent with
the laws of logic.
* \(p\) is *logically necessary* iff \(p\) follows from the
laws of logic.
* \(p\) is *physically possible* iff \(p\) is consistent with
the laws of nature.
* \(p\) is *physically necessary* iff \(p\) follows from the
laws of nature.



It is more controversial how one should define *metaphysical*
modality. The traditional approach appeals to alternative ways the
world might have been, called
 "possible worlds".


* \(p\) is *metaphysically possible* iff \(p\) is true in at
least one possible world.
* \(p\) is *metaphysically necessary* iff \(p\) is true in
all possible worlds.



Alternatively, philosophers have defined metaphysical modality in
terms of *laws of metaphysics* (see, e.g., Kment 2014, 2021;
for discussion: Wilsch 2015, 2020).


* \(p\) is *metaphysically possible* iff \(p\) is consistent
with the laws of metaphysics.
* \(p\) is *metaphysically necessary* iff \(p\) follows from
the laws of metaphysics.



In addition, metaphysical modality has often been characterized as the
*widest*, *strongest*, *most unrestricted*, or
*absolute* modality (e.g., Kripke 1980; Lewis 1986; Stalnaker
2003; van Inwagen 1998; Hale 2013; Williamson 2016). While these are
metaphorical labels (and recently the target of several criticisms,
e.g., Clarke-Doane 2019a, 2019b; Mallozzi forthcoming a), the core
idea is that metaphysical modality is not restricted by the laws of
nature and is more substantive than logical-conceptual modality. As
such, it is plausibly the modality of philosophical thinking *par
excellence*.



A helpful diagram to understand the relationship between the three
main alethic modalities, namely logical, physical, and metaphysical
modality, is the nesting model. The model depicts a nesting relation
among those modalities, such that what is physically possible is also
metaphysically possible, and what is metaphysically possible is also
logically possible (see fig. 1).



![three nested ovals. The innermost one labeled 'Physical', the midmost one 'Metaphysical', and outermost one labeled 'Logical'.](figure.svg)

Fig. 1: Nesting model for
*possibility*.




Conversely, what is logically necessary is metaphysically necessary,
and what is metaphysically necessary is also physically necessary.
Other kinds of modality can be suitably added to the model, as well,
such as practical possibility. Practical possibilities would be within
the physical possibilities. Importantly, some philosophers question
whether metaphysical modality is a distinct and irreducible modality.
Alternative accounts include *inflationism, deflationism*, and
*skepticism*. Inflationists, such as David Chalmers (2002),
hold "Modal Monism", the view that there is only one modal
notion or primitive, such that metaphysical and logical modality
coincide (more below,
 SS4.1).
 Deflationists, such as Sydney Shoemaker (1998), argue that
metaphysical modality coincides with physical modality. Skeptics, such
as Graham Priest (2021), question whether there is a notion of
metaphysical necessity that is distinct from both, *analytic*
necessity (which corresponds to conceptual necessity) and
*physical* necessity.



*Metaphysical modality* is the modality that is typically at
stake in philosophical argumentation (e.g.,
 St. Anselm's Ontological Argument,
 Rene Descartes' Argument for Mind-Body Dualism,
 George Berkeley's Argument for Idealism).
 Accordingly, the Access Question in the epistemology of modality
focuses on how we can access metaphysical modality. Besides
investigating the modal status of philosophical propositions, modal
epistemologists are also interested in answering common every-day
modal questions, such as, *could the couch be on the other side of
the room? Can Mary climb the tree? Can the cup fit in the
drawer?*



Some philosophers have recently approached the epistemology of
metaphysical modality by first investigating whether some every-day
propositions are *practically possible* (as opposed to
metaphysically possible) (e.g., Strohminger 2015 and Vetter
forthcoming). Whether some proposition \(p\) is *practically
possible* hinges on some specific circumstances that are held
fixed in a situation--for example, given a particular
subject's physical abilities, or certain environmental
conditions. While it seems uncontroversial that it is metaphysically
possible to get the couch to the other side of the room, a specific
subject might wonder whether it is practically possible for her to do
so, given certain circumstances.



This raises a Navigation Question: How are we to epistemically
navigate from practical modality to metaphysical modality? Given that
we know that \(p\) is practically possible, how do we come to know
that it is metaphysically possible? Is this done via some (implicit or
explicit) inferential transition? If so, does that imply that we need
knowledge of some bridge principle between practical and metaphysical
possibility?



Here it is useful to see the contrast between the Access Question and
the Navigation Question again. While the former asks how we initially
get epistemic access to the modal realm without relying on modal
premises, the latter asks about how we epistemically navigate from one
"sphere" or kind of modality to another. We will see that
while the Access Question has traditionally been the main focus in the
literature, some recent accounts (like, e.g., Strohminger's
(2015), Vetter's (forthcoming), and, in a sense, Chalmers'
(2002)) a Navigation Question takes center stage.


## 2. Classification Schemes in the Epistemology of Modality



There are many theories of modal knowledge, and many ways to classify
them. In this article we proceed based on the following main
categories:


### 2.1 Mental Capacities and Inferential Methods



The distinction between *mental capacities* and *inferential
methods* is a natural starting point for addressing the Access
Question. The *mental capacities* that are most discussed in
the epistemology of modality are: *conceivability, understanding,
imagination, intuition*, and *perception*. The
*inferential methods* are: *deduction, induction*, and
*abduction*. We will see how those notions are spelled out more
precisely in the different theories. Mental capacities and/or
inferential methods that are central to a theory of modal knowledge
offer a main criterion for classifying theories. Furthermore, theories
of modal knowledge need not restrict themselves to adopting only one
mental capacity or inferential method. In fact, they sometimes combine
them in various ways.



Theories should not only investigate which specific capacities and
methods are involved with modal knowledge, but also in virtue of what
such capacities and methods yield the correct results. Mallozzi
(2021e) accordingly distinguishes between *descriptive* and
*normative* tasks with regard to modal reasoning and modal
knowledge. The descriptive task involves identifying and describing
the belief-formation processes and methods that subjects actually
carry out in modal reasoning (for example counterfactual reasoning, or
deductive inference). The descriptive task does not in itself involve
answering the question of *how* the processes are
truth-conducive. This question takes center stage in the normative
task, which targets the correctness conditions for such processes and
methods. More precisely, a chief normative task for the epistemology
of modality is to elucidate what constrains such processes or methods,
i.e., in virtue of what their outputs are correct or incorrect. As a
normative inquiry, the epistemology of modality is centrally concerned
with what Vaidya and Wallner (2021) call the *Problem of Modal
Epistemic Friction (PMEF).* This problem concerns the normative
restrictions on candidate capacities or methods. Take, e.g.,
*imagination* as a candidate mental capacity in our pursuit for
modal knowledge. In order for us to be properly guided to modal
knowledge, we cannot apply imagination in a completely
*unrestricted* manner. If no restrictions would apply, we could
imagine all sorts of impossible things like water without hydrogen,
transparent iron etc. Hence, some restrictions, or
"*epistemic friction creators*", as Vaidya and
Wallner call them, have to be in place. The PMEF asks what the
epistemic friction creators are and how we come to know them or at
least how we come to adequately deploy them in our application of
various capacities and methods in order to be properly guided to modal
knowledge.



While descriptive tasks and normative tasks are distinct, they need
not be pursued independently. Normative modal epistemology may, for
example, be informed by empirical psychology (the study of
counterfactuals is a prominent example), and vice-versa.


### 2.2 Necessity-First vs. Possibility-First



Hale (2002) draws an important distinction between two different
architectures one can use in building an epistemology of modality.
*Necessity-first* accounts hold that we first acquire knowledge
of necessity and then arrive at knowledge of possibility by inferring
what is *consistent* with what we know to be necessary.
*Possibility-first accounts*, by contrast, hold that we first
acquire knowledge of possibility from which we then generalize to
knowledge of necessity. Most conceivability-based accounts
 (SS4.1)
 implement a possibility-first approach. So do dispositionalist
approaches as well as Roca-Royes' similarity-based account, as
they all prioritize possibilities
 (SS7).
 Counterfactual-based accounts such as Williamson's
 (SS4.2)
 seem instead more neutral concerning the distinction. Finally,
essence-based accounts
 (SS5)
 are usually necessity-first. (For discussion see: Hale (2013),
Roca-Royes (2017), and Fischer (2017)).


### 2.3 Modal Rationalism vs. Modal Empiricism



Kant famously argued that what is *a priori* coincides with
what is necessary, thereby ruling out the category of *a posteriori
necessities*. However, Kripke (1971) pointed out that there are
necessary truths that can only be known *a posteriori*. The
contemporary distinction between modal rationalism and modal
empiricism moves off of Kripke's (1971) deduction model for
knowledge of *a posteriori* necessities. According to Kripke,
we proceed based on the conditional "If \(p\), then necessarily
\(p\)", where "\(p\)" stands for some fact we can
discover via empirical investigation. For example,



(K1)
If Hesperus = Phosphorus, then necessarily (Hesperus =
Phosphorus)
(K2)
Hesperus = Phosphorus
(K3)
Necessarily, (Hesperus = Phosphorus)


(K1)--one
 of the so-called "Kripke conditionals"--is a modal
premise that instantiates "If \(p\), then necessarily
\(p\)", which he suggests is something we know "by *a
priori* philosophical analysis" (1971: 180; 1980: 108). On
the other hand,
 (K2)
 is a non-modal, factual premise that we may come to know empirically.
It was an empirical discovery that the celestial body that we call
"Hesperus" for its evening sightings was the same one as
the one we call "Phosphorus" for its morning sightings,
namely the planet Venus. As a consequence of the empirical
contribution of (K2), the conclusion of the argument,
 (K3),
 is also *a posteriori*. (For further discussion, see Casullo
1977, 2010; Peacocke 1999). Note that not all instances of "If
\(p\), then necessarily \(p\)" will be true. In this paradigm
case, \(p\) is an identity statement involving rigid designators on
both sides. These statements are such that if true, they are
necessarily true, which is something most philosophers hold we can
know *a priori*. (See also the entry on
 rigid designation).



Modal rationalists accept and accommodate Kripkean *a
posteriori* necessities by emphasizing that in a Kripkean
inference
 (K1)-(K3),
 the modal part,
 (K1),
 is known *a priori.* Not all epistemologists endorse a
deductive picture.



In general, *modal rationalists* prioritize *a priori*
methods for acquiring knowledge of metaphysical modality.



By contrast, *modal empiricists* pursue *a posteriori*
accounts of knowledge of metaphysical modality. Often they still
acknowledge that *a priori* methods might contribute to modal
knowledge. (See Fischer & Leon 2017)



Some philosophers have challenged the philosophical significance of
the *a priori*/*a posteriori* distinction (e.g.,
Hawthorne 2007; Sosa 2013; Williamson 2007, 2013; for discussion:
Casullo 2015). We discuss Williamson's version of the challenge
in
 SS4.2.


## 3. Skepticism and Knowability



Skepticism about modal knowledge has received attention in the
literature since van Inwagen's (1998) seminal paper. In this
entry we largely assume that one can have some knowledge (or
*justified belief*) about modality. We will only briefly
present the issues and refer to the relevant literature for further
discussion.



There are two broadly skeptical challenges in the contemporary
literature.



*The Integration Challenge* (Peacocke 1999): This challenge is
modelled after the Benacerraf Problem for
 Platonism in the philosophy of mathematics.
 According to Benacerraf (1973) any robustly realist (platonist)
stance about mathematical objects like numbers regards them as
abstract entities outside of space and time, i.e., as
"platonic" entities. As such, they seem inaccessible to
us. Unlike ordinary perceptible objects, to which we have a causal
connection, it is unclear how we might detect platonic entities in
order to know about them, since we have no causal connection to them.
The possibilities and necessities that modal statements are about also
seem to be outside of space and time and thus our epistemic access to
them seems mysterious. So, on a par with the Benacerraf Problem in the
philosophy of mathematics, the Integration Challenge in the philosophy
of modality consists in providing a plausible account of how we know
modal statements, which at the same time fits our modal metaphysics
(see, e.g., Bueno & Shalkowski 2000; Fischer 2018; Roca-Royes 2020
for discussion).



*The Reliability Challenge* (Nozick 2001): If we are to be
justified in believing modal statements, we must have a reliable
faculty or a set of reliable faculties working together for forming
beliefs of that sort, the existence of which is best explained by
evolutionary theory. No ad hoc modality-detecting faculty is allowed
for explaining modal knowledge. The Reliability Challenge instantiates
the desiderata of what is sometimes called
"anti-exceptionalism" in modal epistemology, according to
which



> 
> 
> our knowledge of metaphysical modality is *continuous* with our
> everyday knowledge about the world. (Vetter 2016: 766)
> 
> 
> 



Skepticism about *extraordinary* or *philosophical*
cases varies across theories. Van Inwagen (1998) voices skepticism
about extraordinary cases by an analogy with vision. We do and should
withhold judgment concerning what we see, when it is outside the range
of reliability in our field of vision. For the farther out objects are
in our field of vision, the less reliable we are at judging them.
Similarly, we ought to withhold judgment concerning what we conceive
or imagine or infer about modal reality, when they are outside the
range of reliability of the specified capacity or method (for
discussion: Barnes 2002, Geirsson 2005, and Strohminger &
Yli-Vakkuri 2018).



Van Inwagen's moderate skepticism draws attention to the issue
of the *scope* of our modal knowledge. Which modal propositions
are knowable, if any? We can ask whether a certain account targets
knowledge of just one kind of modality, or more. Focusing on one kind
of modality, we can also ask whether a given theory aims to account
for our access to *the whole range of* (knowable) modal
propositions (from the every-day ones to the philosophical ones, from
those about abstracta to those about concreta, etc.), or merely to
some of them. In the former case the theory might be labeled
*ambitious*, in the latter, *modest* (see Wirling 2020).
Some modest theories, for instance, aim to offer an account of
ordinary modal knowledge, which involves what is possible and
necessary for couches and cups, say; but they are either skeptical or
silent about extraordinary or philosophical cases, such as whether the
number 2 could have been the number 3 or whether there could have been
philosophical
 zombies--i.e.,
 a creature that is physically identical in every respect to a human
being but lacks all phenomenal consciousness.


## 4. Conceivability, Imagination, Intuition, and Understanding



Historically, the notions of *imagination, conceivability,
intuition*, and *understanding* have been prominent in
explaining modal knowledge. For Descartes, the source of our modal
knowledge is a distinctive sort of intellectual grasp based on
understanding, which might be interpreted as a kind of conceiving, or
intuiting. For Hume, it is imagination as an experientially-informed
cognitive faculty that is a guide to knowledge of possibility (see
Gendler & Hawthorne 2002). This Humean tradition has been pursued
in the early stages of post-Kripkean discussions of the epistemology
of modality by a number of authors, and it has maintained a central
role in more recent discussions.


### 4.1 Conceivability



In ordinary pre-theoretical talk, "conceiving" and
"imagining" may well be used interchangeably; and often
philosophers, too, treat those terms roughly as synonymous. In the
literature on the epistemology of modality, however,
*conceivability* is a technical notion, which may be defined in
different ways. These are mainly stipulative choices, but it is
important to flag terminological variations across different
theories.



Both Stephen Yablo (1993) and David Chalmers (1996, 2002, 2004, 2010:
Ch. 6) have developed independent accounts of conceivability as a
source of modal knowledge (for yet another account based on
*response-dependence*, see Menzies 1998). Yablo holds that,
when adequately understood, conceivability provides defeasible
evidence for possibility. In Yablo's account, the relevant
notion of conceivability involves the *imaginability* of a
situation in which a conceived *proposition is taken to be true by
the subject in question*. Yablo offers the following two
conditionals for describing the appropriate *philosophical*
notion of conceivability which provides evidence of possibility (1993:
29)



(CON)
\(p\) is conceivable for \(X\), if \(X\) can imagine a world that
\(X\) takes to verify \(p\).
(INC)
\(p\) is inconceivable for \(X\), if \(X\) cannot imagine any
world that \(X\) takes to verify \(p\).


Yablo's *philosophical conceivability*
(CON),
 involves imagining a world that one takes to verify some proposition
\(p\). Note that when imagining a world, we don't need to
specify all the details in the world in imagination. The imagining
provides *prima facie* evidence for the possibility of \(p\)
because it involves what Yablo calls an "*appearance of
possibility*" (i.e., it seems as if \(p\) is possible, given
the imagined world). "[T]o imagine an \(X\) is thereby to enjoy
the appearance that an \(X\) could exist" (1993: 30).



Importantly, for Yablo, conceivability, thus understood, helps address
a pressing challenge from the post-Kripkean literature, namely the
issue of *modal error*. This is the issue of explaining what
the sources of our erroneous modal judgments are (see, e.g., Bealer
2004 and Yablo 2006). While modal error can in principle affect both
*a priori* and empirical modal reasoning, Yablo focuses on the
challenge to conceivability as a guide to possibility that arises from
Kripke's cases of the necessary *a posteriori*. Not being
aware of the fact that Hesperus is Phosphorus, I might find it
conceivable that one exists without the other; thereby I conclude that
it is possible for Hesperus to exist without Phosphorus. But that is a
modal error. So how does Yablo's conceivability do us any good?
For him, conceivability-based evidence is positive defeasible evidence
of possibility. When properly understood as specified by
 (CON),
 conceivability confers *prima facie* justification for the
modal belief in question. Yablo draws an analogy with
*perception*, which is also a fallible source of knowledge. He
argues that in the case of perception, the possibility of error and
illusions does not keep us from assigning *prima facie*
justification for beliefs based on perception. Similarly, the
possibility of modal error in conceivability does not undermine the
thesis that conceivability provides *prima facie* evidence for
possibility. Although for Yablo there is a difference between
conceivability and perception that makes the former provide more
doubtful evidence, the difference is not a matter of fallibility or
likelihood of error. Rather, the difference for Yablo lies in the fact
that we have a much better story of how perceptual error comes about
compared to modal error (see also van Inwagen's 1998 discussion
of modal skepticism based on the analogy with vision, as well as
Bealer 2004 for discussion of the sources of modal error). This is
also true of debates about intuition as a source of justification (see
Weinberg 2007). However, while Yablo's notion of philosophical
conceivability can answer criticism based on the possibility of modal
error, he concedes that more work needs to be done to produce an
exhaustive account of modal error that will best guard us against
it.



Chalmers (1996, 2002, 2010: Ch. 6) affirms an even stronger link
between conceivability and possibility than Yablo. When adequately
understood, conceivability *entails* possibility, as opposed to
merely providing evidence for possibility. More precisely, the main
thesis of Chalmers' *Weak Modal Rationalism* is



(WMR)
*Ideal, positive, primary conceivability entails primary
possibility:*


(WMR)
 is constructed out of three distinctions:


1. *prima facie* vs. *ideal* conceivability
2. *positive* vs. *negative* conceivability
3. *primary* vs. *secondary* conceivability and
possibility



*Prima facie* conceivability is one's initial assessment
of whether a described hypothesis is possible, without engaging in
careful reasoning about the hypothesis. Better reasoning often gives
one reason to doubt *prima facie* conceivability.
*Ideal* conceivability, by contrast, involves a kind of
reasoning that cannot be weakened by further reasoning. If some
proposition is ideally conceivable, then that proposition is the case
from the perspective of a hypothetical reasoner who is "free of
all cognitive limitations" (Chalmers 2002: 148) and free from
error due to lack of attention. For Chalmers this is sufficient for
ideal reasoning to be safe from modal error. This is why, for
Chalmers, an *entailment* link between conceivability and
possibility can be forged only when *ideal* conceivability is
in play.



*Positive* conceivability amounts to coherently imagining a
scenario in which something is the case. The aim is to "form
some sort of clear and distinct conception of a situation in which the
hypothesis is true" (Chalmers 2010: 144). It need not be a
*complete* description of a scenario, but it must be
sufficiently detailed so as to verify the statement being considered.
By contrast, *negative* conceivability is the inability to
*a priori* rule out a certain scenario. That is, negative
conceivability amounts to one's inability to rule out a
possibility as incoherent based on what one knows. This is often
weaker than positive conceivability, since it often derives from
ignorance of the relevant facts. For example, if one does not know
that water is H2O, they may find the statement "water
might not contain hydrogen" conceivable because they cannot rule
out the statement as *a priori* incoherent. Conceiving of water
without hydrogen in the *positive* sense, on the other hand,
requires constructing a scenario in which water is present without
hydrogen at the relevant depth of detail required to verify the claim.
Arguably, that sort of scenario cannot be constructed once one knows
the relevant empirical facts, since if they are attentively engaged in
the construction they will notice a contradiction between water being
H2O and hydrogen being absent.



Finally, the distinction between *primary* and
*secondary* conceivability and possibility pertains to
Chalmers' version of
 Two-Dimensional Semantics.
 His *Epistemic Two-Dimensional Semantics* (E2-D) proposes a
way to address the challenge posed by Kripkean *a posteriori
necessities*, namely the apparent problem that *a
posteriori* impossibilities like "water is not
H2O" seem conceivable. In response, Chalmers holds
that "water is not H2O" is not
*secondarily* conceivable, though it is still
*primarily* conceivable. What exactly does this mean?



The main idea of (E2-D) is that there are two different ways in which
we can evaluate statements across possible worlds, i.e., two different
ways of conceiving hypothetical situations, based on two different
constraints.



The first constraint binds what is true in some possible world to what
one knows *a priori*. A statement is primarily conceivable if
nothing that is knowable *a priori* is incompatible with the
statement being true. As Chalmers explains, that captures a kind of
*epistemic* possibility. Consider again the statement
"water is not H2O". The actual chemical
composition of water, H2O, is not knowable *a
priori*. So this fact does not constrain what is true in the
possible worlds in which the existence of water is *a priori*
conceivable. Accordingly, "water is not H2O" is
*primarily conceivable*. As Chalmers also puts it, primary
conceivability amounts to coherently conceiving the situation
described as *actual*, namely as a way the world might turn out
to be.



By contrast, it has been discovered empirically that water is
H2O. The second constraint binds what is true at other
possible worlds to facts about how things actually are. As Chalmers
explains, that captures a kind of *subjunctive* possibility.
Since chemical composition is arguably essential to substances, such
as water, it is not *secondarily conceivable* that water is not
H2O. As Chalmers also puts it, secondary conceivability
amounts to coherently conceiving the situation described as
*counterfactual*, namely as a way the world might have been,
given how our world is. Thus:



(PrimC)
A statement \(S\) is *primarily* conceivable when it is
conceivable that the situation described in \(S\) is *actually*
the case.
(SecC)
A statement \(S\) is *secondarily* conceivable when it is
conceivable that the situation described in \(S\) might
*counterfactually* have been the case. (cf. Chalmers 2002:
157)


To further clarify, for Chalmers expressions have two dimensions of
meaning or content: a *primary intension* and a *secondary
intension*. In the case of sentences describing Kripkean a
posteriori necessities like "water is H2O",
these are two different propositions. The primary intension of an
expression like, e.g., "water", picks out a referent at a
world considered as actual; namely, roughly based on the descriptive
content that a speaker *a priori* associates with the
expression. Thus, at any world we consider, the primary intension of
"water" picks out whatever substance satisfies some
description such as "the liquid drinkable stuff in lakes and
rivers etc." (or, otherwise put, whatever plays the water role).
At any world we consider as actual, "water" will pick out
such a substance. Secondary intensions, by contrast, pick out the
referent of an expression at a world considered as counterfactual,
namely based on the way a speaker evaluates a given expression
*counterfactually*, given how the actual world is. That
requires acknowledging that water is H2O. Assuming, as
usual, that having a certain chemical composition is essential to
being a certain kind of substance, the secondary intension of
"water" picks out H2O compounds at all worlds
(otherwise put, it picks out what actually plays the water role). At
any world we consider as counterfactual, "water" will pick
out H2O. Accordingly, sentences like "water is
H2O" are *secondarily* necessary but
*primarily* contingent. For, while it is possible that the
liquid drinkable stuff in rivers and lakes etc. is not H2O,
it is not possible that water isn't H2O. Thus,
according to Chalmers, ideal positive primary conceivability allows us
to access a specific kind of possibility, namely primary possibility,
which are sometimes secondarily impossible. While there is a primary
possibility in which water isn't H2O, there is no
secondary possibility in which water isn't H2O.



However, primary possibility is no less "real" than
secondary possibility. Chalmers argues that there is only one space of
worlds or that "conceptual=logical=metaphysical possibility (at
the level of worlds)" (1999: 478). This is what he calls
"Modal Monism". What varies, within modal space, is not
the *kind* of worlds we are considering (namely
"merely" logically-conceptually possible versus
"genuinely" metaphysically possible); but rather the
truth-values of the expressions under examination at a given world,
depending on whether we consider their primary or secondary
intensions. Because of Modal Monism, within Chalmers' framework
every primary possibility is thus a *metaphysical* possibility,
though it might not be a secondary possibility. "Water is not
H2O" is ideally positively primarily conceivable, and
therefore primary possible. Given Modal Monism, Chalmers can thus
argue that "water is not H2O" is a
*metaphysical* possibility, while also resisting the challenge
posed by the Kripkean *a posteriori* necessities. For
"water is not H2O" is a primary possibility but
not a secondary possibility, given that "water" actually
picks out H2O.



So, by adopting Modal Monism, Chalmers places primary possibility
within the same modal realm as secondary possibility. This guarantees
that primary possibility is no less "real" or
"genuine" than secondary possibility (indeed, as Chalmers
puts it, "these worlds are all first-class metaphysical
possibilities" [2002: 165]) Thus, the kind of possibility that
is entailed by primary, positive, ideal conceivability, is a
metaphysical one.


#### Critical Questions for Conceivability



**The Connection Question:** This is the central question
that conceivability theorists like Yablo and Chalmers try to answer.
How is conceivability connected to possibility? Given that
metaphysical modality is an objective modality that is
mind-independent, while conceivability is subject-sensitive and
mind-dependent, how are the two connected such that conceivability may
entail, or at least provide evidence for possibility? Answering the
Connection Question should thus clarify how mind-dependent
conceivability may provide one with justification for believing that
something is mind-independently possible.



**The Scope Question:** This question further specifies
the Connection Question, by asking how conceivability can effectively
cast light on matters of *metaphysical* possibility, as opposed
to *logical-conceptual* possibility. Remember that primary
conceivability is a purely *a priori* exercise based on
considerations of (ideal) logical and conceptual coherence of a
described scenario. What ensures that conceivability exercises so
constrained successfully capture metaphysical modality? Within
Chalmers' framework: what ensures that primary possibilities are
themselves metaphysical possibilities? Several philosophers have
argued that assuming Modal Monism is not a satisfying answer (for
discussion: Soames 2004; Vaidya 2008; Mallozzi 2021b).



**The Navigation Question:** Granted
 (WMR),
 we might still wonder about knowledge of *secondary*
possibility. Is there any *a priori* way of inferring secondary
possibility from primary possibility? Simply put: can we *navigate
a priori* from primary to secondary possibility? Chalmers thinks
that in some special cases we can. Such cases require that an
expression's primary and secondary intensions *coincide.*
Candidate examples include, most notably, the class of phenomenal
truths as well as mathematical and analytic truths (Chalmers 2010: ch.
6). However, that raises a worry that on Chalmers'
conceivability theory we won't be able to have *a priori*
access to most of the modal metaphysical realm. Conceivability seems a
limited resource for knowledge of metaphysical modality.



**The Dependence Question:** Suppose conceivability does
provide justification for believing that something is possible. Does
it succeed in doing so because conceivability operates on some prior
beliefs about the considered scenario? For example, does
conceivability guide one to the belief that a round square is
impossible because one knows what squares and circles are, and by
examining their definition one can arrive safely at the conclusion
that such objects are impossible? Similarly, does one simply find
water in the absence of hydrogen possible because one either
suppresses the knowledge that water contains hydrogen or one does not
know that water does contain hydrogen? In the first case,
conceivability would seem to depend, to an important extent on,
underlying linguistic or conceptual knowledge (along the lines of
analytic accounts of the *a priori* more generally). In the
second case, conceivability would depend on both linguistic or
conceptual knowledge and empirical knowledge. In both cases,
additional essentialist knowledge might be needed (e.g., Kment 2021;
Goff 2021; and Roca-Royes 2011a). In Vaidya and Wallner's
(2021),
 (SS2),
 the critical point of the Dependence Question is the following: In
order for our conceivability exercises to appropriately justify our
modal judgments, those conceivability exercises need to be constrained
by some crucial information about the (essence of) the entities
involved in them, creating the needed *epistemic friction* for
conceivability. In effect, the Dependence Question is concerned with
the issue of the source of modal knowledge. Is conceivability an
*ultimate* source of modal knowledge, or is it derivative,
namely dependent on another source, such as linguistic or conceptual
knowledge and essentialist knowledge? (see also Berto & Schoonen
2018).



**The Human Capacity Question**: Conceivability theorists
hold that, under appropriate conditions, conceivability provides
justification for believing that something is possible. We saw how
Yablo and Chalmers spell out such conditions in presenting their
respective notions of conceivability. But clarifying what the relevant
conditions are for conceivability to yield modal knowledge still
leaves open an important question. Do humans ever satisfy those
conditions? For example, one might agree with Chalmers that some ideal
sort of conceivability entails possibility, but also question whether
we can satisfy the requirements of *ideal* rational reflection
(see, e.g., Worley 2003 and Martinez 2013).



**The Relevant Depth Question**: This targets the content
of the imagined situation or world that the subject takes to verify
some proposition \(p\). In what *detail* do we have to imagine
a world \(w\) in order for the fact that \(p\) seems true in \(w\) to
confer evidence for the possibility of \(p\)? (see van Inwagen 1998)
The issue of *relevant depth* has to do with what imagined
details are needed to justify a possibility judgment, e.g., is it
enough to imagine a human brain functioning normally while not having
any experiences to justify the possibility of a philosophical
zombie?



**The Self-Defeat Question:** Suppose that some thesis
according to which a certain sort of conceivability entails a certain
sort of possibility--call it (CP)--is true. Is it then
*conceivable* that (CP) is false? If that is conceivable, or so
Howell (2008) and Mizrahi and Morrow (2015) have argued, then, by
(CP), it is possible that (CP) is false. However, if (CP) is possibly
false, (CP) is actually false. For a counterexample to the entailment
relation falsifies the entailment relation. Thus, if we can conceive
of (CP) failing, it follows that (CP) is self-defeating.


### 4.2 Counterfactual Imagination



Timothy Williamson (2007) has developed a theory of modal knowledge
based on our capacity for counterfactual reasoning, which
distinctively deploys *imagination* in the development of a
counterfactual. The topic of
 imagination
 has gained widespread attention in contemporary debates within
philosophy, logic, and the cognitive sciences. The focus has been on
the epistemic uses of imagination for both quotidian non-modal
knowledge (e.g., knowledge of others' mental states, learning,
planning and decision making) as well as various kinds of modal
knowledge (see, e.g., Currie & Ravenscroft 2002; Kind & Kung
2016; Kind 2020; Badura & Kind 2021; Kosslyn, Ganis, &
Thompson 2003; Nichols 2006). Theories of modal epistemology that rely
to various extents on imagination need not be rationalist; in fact,
they are often empiricist. Here we only discuss Williamson's
counterfactual imagination account. For further work on
imagination-based accounts, whether rationalist or empiricist, see,
e.g., Gregory (2004, 2010, 2020), Byrne (2007), Kung (2010), Ichikawa
and Jarvis (2012), Casullo (2012a), and Lam (2018) (On the other hand,
note that Hill 2006, Kroedel 2012, and Kment 2014 have offered
theories of modal knowledge that variously appeal to counterfactuals
and counterfactual reasoning, which do not centrally involve
imagination).



Williamson's central thesis is that knowledge of metaphysical
modality is a "special case" of knowledge of
counterfactual conditionals. As he puts it,



> 
> 
> the ordinary cognitive capacity to handle counterfactual conditionals
> carries with it the cognitive capacity to handle metaphysical
> modality. (2007: 136)
> 
> 
> 



The capacity for modal knowledge can thus be thought of as a byproduct
of our capacity for counterfactual thinking. For Williamson
counterfactual thinking is largely imaginative thinking. When we
assess a given counterfactual, we evaluate the consequent on the
supposition of the antecedent by developing the supposition through an
*imaginative* exercise. This typically involves the
"offline" application of our cognitive capacities. More
precisely, Williamson holds that in imagination we often transpose
"online" cognitive skills that are originally developed in
perception into corresponding offline cognitive skills (2013).



Williamson supports the thesis that knowledge of metaphysical modality
is a special case of imaginative counterfactual knowledge with logical
equivalences between sentences using counterfactual operators and
modal operators, aimed at showing that statements of possibility and
necessity can be reformulated in counterfactual terms in a
straightforward way:



(NEC)
\(\Box A \text{ iff } (\neg A \boxarrow \bot)\)
  

(it is necessary that \(A\) *iff* if it were not the case that
\(A\) a contradiction would follow)
(POS)
\(\Diamond A \text{ iff } \neg (A \boxarrow \bot)\)
  

(it is possible that \(A\) *iff* it is not the case that if
\(A\) were true a contradiction would follow)


Thus, we can identify the following two key theses in
Williamson's counterfactual theory:



* *Logical Equivalence*: metaphysical possibility and
necessity can be proven to be logically equivalent to counterfactual
conditionals.
* *Epistemic Pathway*: the method of counterfactual
development carried out in imagination can provide one with knowledge
of metaphysical modality.




The two are importantly interconnected in that *Epistemic
Pathway* is partly based on *Logical Equivalence.* As
Williamson puts it,



> 
> 
> modulo the implicit recognition of this equivalence, the epistemology
> of metaphysically modal thinking is tantamount to a special case of
> the epistemology of counterfactual thinking. (2007: 158)
> 
> 
> 



Relying on equivalences
 (POS)
 and
 (NEC),
 we come to know about possibility and necessity by developing
counterfactual suppositions in imagination in a search for a
contradiction.



In order to see how this works, let us first look at an evaluation of
an "ordinary" every-day counterfactual. Consider the
following example from Williamson:



> 
> 
> Suppose that you are in the mountains. As the sun melts the ice, rocks
> embedded in it are loosened and crash down the slope. You notice one
> rock slide into a bush. You wonder where it would have ended if the
> bush had not been there. A natural way to answer the question is by
> visualizing the rock sliding without the bush there, then bouncing
> down the slope into the lake at the bottom. Under suitable background
> conditions, you thereby come to know the counterfactual:
> 
> 
> 
> (Rock)
> *If the bush had not been there, the rock would have ended in
> the lake* (2007: 142)
> 
> 



As Williamson explains, the general procedure we use to arrive at
 (Rock)
 is the following:



> 
> 
> [O]ne supposes the antecedent and develops the supposition, adding
> further judgments within the supposition by reasoning, offline
> predictive mechanisms, and other offline judgments. The imagining may
> but need not be perceptual imagining. All of one's background
> beliefs are available from within the scope of the supposition as a
> description of one's actual circumstances for the purposes of
> comparison with the counterfactual circumstances... Some but not
> all of one's background knowledge and beliefs are also available
> within the scope of the supposition as a description of the
> counterfactual circumstances, according to complex criteria... To
> a first approximation: one asserts the counterfactual conditional if
> and only if the development [of the antecedent] eventually leads one
> to add the consequent. (2007: 152-153)
> 
> 
> 



The same procedure can be applied to evaluate the counterfactuals that
figure in
 (NEC)
 and
 (POS),
 in order to gain modal knowledge. Based on the logical equivalence in
(POS), we can come to know "\(\diamond A\)" by knowing
"\(\neg(A \boxarrow \bot)\)". And we know the latter
through a counterfactual development, much like in the
 (Rock)
 example. For example, we might assess whether it is
*metaphysically possible* for the rock to have ended in the
lake, by using the logical equivalence (POS). The simple procedure
will be to counterfactually suppose that the rock did end in the lake
and check whether a contradiction would follow, as we develop that
supposition in imagination as "realistically" as we can
(2007: 142).



(Rock-POS)
If the rock had ended in the lake no contradiction would have
followed.


If
 (Rock-POS)
 is true, we are warranted in asserting that it is metaphysically
possible for the rock to have ended in the lake.



In addition, based on the logical equivalence
 (NEC),
 we can come to know "\(\Box A\)" by knowing "\(\neg
A \boxarrow \bot\)". And we know the latter through a
counterfactual development of the antecedent of the counterfactual
("\(\neg A\)"), much like in the
 (Rock)
 example. If the counterfactual development of "\(\neg
A\)" yields a contradiction (i.e., the consequent of the
counterfactual in question), we assent to the counterfactual and
thereby come to know that A is necessary. To take another example from
Williamson:



> 
> 
> If we know enough chemistry, our counterfactual development of the
> supposition that gold is [not] the element with atomic number 79 will
> generate a contradiction. (2007: 164)
> 
> 
> 



We thereby come to know that it is necessary that gold is the element
with atomic number 79.



On Williamson's account we can generally trust our capacity for
assessing counterfactual conditionals in imagination, as this is
informed and disciplined by a great amount of background knowledge
concerning the workings of nature. This background information
includes general knowledge of chemical, physical, and other basic
scientific facts, as well as some grasp of the causal and natural
laws. On any given occasion, we keep some of this background knowledge
fixed within the scope of the supposition as we carry out our
counterfactual evaluations. Goodman's (1955) classical
*problem of cotenability* concerns the question of
*which* facts or beliefs are cotenable with the antecedent of
the counterfactual conditional. That is, which facts or beliefs are to
be held fixed in a counterfactual development? As we will see, many
have raised concerns about what to count as cotenable when evaluating
a counterfactual supposition. Crucially, background knowledge also
involves some grasp of "constitutive" facts, as Williamson
sometimes calls them. These apparently include essentialist facts and
principles--for example, Williamson mentions Kripke's
principle of the necessity of origins, which holds that the material
origins of an entity are essential to it.



There is also a more general reason why Williamson's method for
modal knowledge should be reliable. Williamson stresses that knowledge
of counterfactuals is pervasive for human decision-making, planning,
and theory construction in science (2007). In his (2016) he further
conjectures that imagination as a source of knowledge might even have
given us an evolutionary advantage as a species, as opposed to being a
mere accidental byproduct of our evolutionary history. Thus, insofar
as modal knowledge proceeds via the reliable method of counterfactual
development in imagination, we should also rest assured that we will
get at the right answers concerning matters of metaphysical modality.
(Note that this may offer an answer against Nozick's 2001
evolution-based skepticism about our knowledge of metaphysical
modality).



Furthermore, for Williamson modal knowledge typically has a special
epistemic status which is *in between* the *a priori*
and *a posteriori* categories. In Williamson's
terminology, the kind of knowledge in question is
"armchair". That is, on the one hand, the knowledge in
question isn't strictly *a posteriori*, since apparently
we can't fully derive it from empirical experience. And, on the
other hand, such knowledge doesn't fit the model of *a
priori* knowledge, either, since arguably background information
from science, and experiential contribution more generally, plays a
role that goes beyond merely enabling concept possession and use.
Williamson also contends that the *a priori / a posteriori*
distinction is in general too superficial or it "doesn't
cut at the epistemic joints" (2013: 8. For discussion, see e.g.
Boghossian 2011, Boghossian and Williamson 2020; Casullo 2013; Jenkins
2008; Mallozzi 2021d; Malmgren 2011).



Williamson's view straddles the division between
*rationalist* and *empiricist* accounts. Thus, for
Williamson we can gain knowledge of metaphysical modality thanks to a
combination of


1. our capacity for carrying out counterfactual reasoning in
imagination, as constrained by our background knowledge of the world
(*Epistemic Pathway*),



together with


2. suitable logical equivalences that guarantee that modal statements
are equivalent to counterfactual statements (*Logical
Equivalence*).


#### Critical Questions for Counterfactual Theory



We can divide the central critical questions for Williamson's
counterfactual theory based on whether they target (*Epistemic
Pathway*) or (*Logical Equivalence*) more specifically. We
start with the latter.


##### Against (*Logical Equivalence*)



**The Counterpossibles Question:** Some philosophers
question Williamson's purported logical equivalence between
counterfactual statements and modal statements (Berto, French, Priest,
& Ripley 2018; Jago 2021). Particularly, in order for
 (NEC)
 to hold, one has to accept that all counterpossibles (namely
counterfactual conditionals with impossible antecedents) are vacuously
true. But this is controversial. Many have given arguments defending
false counterpossibles based on modal semantics that include
impossible worlds (e.g., Berto et al. 2018; Brogaard & Salerno
2013; Jago 2013; Nolan 1997; Restall 1997). Questioning the truth of
Williamson's logical equivalences might constitute a challenge
for the overall theory of modal knowledge, since, as we saw,
(*Epistemic Pathway*) is partly based on (*Logical
Equivalence*).


##### Against (*Epistemic Pathway*)



**The Epistemic Fallacy Question:** Some contend that
even if Williamson's purported equivalences are true, it
doesn't follow that we know metaphysical modality through the
same cognitive processes by which we know counterfactual conditionals
(Jenkins 2008; Casullo 2012b; for discussion see Yli-Vakkuri 2013).
Modal reasoning might well require using different cognitive-epistemic
methods than those we supposedly employ in counterfactual reasoning.
For example, imagination might not play an epistemic role in the
acquisition of modal knowledge. Appealing to a logical equivalence,
while perhaps necessary, is not sufficient for establishing the
correct epistemology. Otherwise put, (*Logical Equivalence*)
doesn't suffice for (*Epistemic Pathway*).



**The Circularity Question:** Several authors have
critically pointed out that Williamson's method of
counterfactual evaluation appears to rely on pre-existing knowledge of
what Williamson sometimes calls "constitutive facts".
These are most commonly taken as facts about the *essence* of
objects. Now, if we take essentialist facts to be modal in that the
essence of something is the way it must be, this reliance is
problematic for it might make Williamson's epistemology of
modality circular (see, e.g., Boghossian 2011; Tahko 2012; Roca-Royes
2011b). In response, Williamson might contend that his account is not
meant to reduce modal knowledge to counterfactual knowledge, but
rather only to clarify how the one may be a special case or byproduct
of the other (Morato 2019). Furthermore, Williamson might hold that
subjects need not have explicit modal knowledge in order to carry out
their counterfactual evaluations, namely they need not know that some
facts are necessary. Instead, subjects only need to be somehow
reliably sensitive to those facts (Yli-Vakkuri 2013; for discussion
see Vaidya & Wallner 2021).



**The Normative Constraints Question:** Let us assume
that there is no real threat of circularity for Williamson's
account. Several authors point out that the background knowledge that
one needs to keep fixed in our counterfactual evaluations is still
problematic in a number of ways. One classical question concerning the
evaluation of counterfactuals is the *problem of cotenability*.
Which facts or beliefs are *cotenable* with the antecedent of
the counterfactual conditional? Which background knowledge or
information do we hold fixed? For example, to investigate the
counterfactual "If the bush had not been there, the rock would
have bounced into the lake" we imaginatively consider what would
happen to the rock if the bush had not been there. To do this, we
imagine a scenario without the bush. That is, we dispense with the
fact that the *bush* blocks the rock. However, do we also
dispense with the fact that *something* (else) blocks the rock?
We might hypothesize that some other obstacle gets in the way. If we
retain this fact as we develop the scenario, then the rock would have
stopped anyway. Yet the truth in the story that Williamson is assuming
is that the rock would have bounced into the lake. So we must not hold
fixed the fact about an obstacle. Why not, though? What principle
determines that in Williamson's example it is a mistake to hold
fixed the obstacle fact but correct to hold fixed facts like the
momentum of the rock and the presence of the lake?



Williamson broadly appeals to our "sense of how nature
works", which includes for example some general knowledge of
chemistry and physics ("folk" physics as Williamson says),
some grasp of the causal laws, as well as, more tentatively, certain
constitutive or essentialist facts or principles. But it is not clear
what exactly goes into this list, and most importantly in virtue of
what. Williamson's account arguably leaves the Problem of Modal
Epistemic Friction (see
 SS2)
 unanswered. In addition, Tahko (2012) wonders how we should select
the relevant background knowledge and constitutive facts when that
involves deciding between rival scientific hypotheses. Similarly,
Roca-Royes (2011b, 2012) questions not only whether we possess
constitutive knowledge (say, of atomic numbers); she also remarks
that, even if we do possess such knowledge, it is unclear what
cognitive mechanisms are responsible for us reliably telling apart the
constitutive facts from the non-constitutive facts. More generally,
Mallozzi (2021e) argues that while Williamson's account offers
an important empirical hypothesis concerning the cognitive
(imaginative) processes involved with modal reasoning, it overlooks
crucial normative questions for the epistemology of modality, which
involve clarifying what the relevant constraints on modal reasoning
are, and why they count as correct.



**The Scope Question:** Several authors doubt that
Williamson's theory successfully accounts for knowledge of
metaphysical modality, particularly as opposed to causal-nomological
modality. For example, Lowe (2012) argues that since counterfactual
knowledge is strictly causal-nomological knowledge, Williamson's
theory may only explain the latter, and not knowledge of metaphysical
modality. The idea is that Williamson can't really explain how
we know that water is necessarily H2O unless he explicitly
brings in extra principles--e.g., essentialist principles (for
further arguments to the same effect see, e.g., Deng 2016; Gregory
2017; Tahko 2012; and Thomasson 2021).


### 4.3 Intuition and Understanding



The epistemology of modality is importantly connected to the
epistemology of the
 *a priori*,
 as many believe that at least some modal knowledge is purely *a
priori* (*modal rationalism*). Some philosophers have
proposed that either
 intuition
 or understanding, or both of them combined, can provide an account of
*a priori* knowledge and justification, which may be fruitfully
applied to the epistemology of modality. Others have explicitly
offered an intuition-based or understanding-based account of modal
knowledge. (For an empirically informed discussion of intuition see
entry on
 experimental philosophy.)



Philosophers such as Bealer (1998, 1999a,b ), BonJour (1997), Pust
(2000), Huemer (2001, 2005), Koksvik (2011), and Chudnoff (2013), have
developed accounts of the *a priori* that appeal to intuition
as the source of *a priori* knowledge and justification. Most
of them take intuition to form a natural kind of *seeming*
state that is non-reducible to either belief or inclinations to
believe; rather it is *sui generis*. On the other hand,
philosophers like Boghossian (1996, 2000), Jackson (2000); Hale and
Wright (2000); and Peacocke (1999, 2000) have highlighted various ways
in which appealing to understanding of meaning may contribute to
explaining *a priori* knowledge and justification. Here we
discuss a few accounts that directly connect the epistemology of the
*a priori* with the epistemology of modality.



According to BonJour, intuition is a direct grasp or "rational
insight" into "the necessary character of reality"
(1997: 107). This occurs when we "see or grasp or apprehend in a
seemingly direct and unmediated way" (1997: 101) the necessity
of a proposition. This grasping "depends upon nothing beyond an
understanding of the propositional content itself" (1997: 102).
By explicitly providing knowledge of necessity, intuition, as cashed
out by BonJour, is thus a main source of modal knowledge.



Importantly, many that defend intuition hold that they are fallible
and revisable, and arguably only reliable in certain domains. Still,
intuitions minimally provide *prima facie justification*, which
might be defeated by further reasoning or empirical evidence. As
applied to modal knowledge, intuitions provide at least *prima
facie a priori* justification for our modal beliefs and/or for
some basic essentialist principles. For example, consider (RG):



(RG)
Nothing can be red all over and green all over at the same
time.


BonJour maintains that we directly grasp the necessity of
 (RG).
 For him, (RG) is self-evident or just *seems* necessarily
true. So, on the view that intuitions justify, our intuitions provide
at least *prima facie* justification for (RG). (See Levin 2007
for skepticism about the justificatory status of intuitions in
relation to essentialism, such as the essentiality of origins or
fundamental kind; for further discussion see
 arguments for origin essentialism
 in the entry on
 essential vs. accidental properties.)



George Bealer (1996, 1998, 1999a,b, 2002; Bealer in Bealer &
Strawson 1992) integrates understanding and intuition in order to
explain knowledge of modality. As an intuitionist, Bealer takes
intuitions to count as (*prima facie*) evidence. According to
Bealer's *Modal Reliabilism* "something is a basic
source of evidence iff it has an appropriate kind of reliable tie to
the truth" (Bealer 1999a: 34). He articulates a notion of
*determinate understanding* (or determinate concept possession)
that casts light on how our modal intuitions can be appropriately
truth-tracking and, thus *reliable*. Roughly, *determinate
understanding* (or concept possession) excludes any partial
misunderstanding or incomplete understanding of the concept(s) in
question. It ultimately amounts to a form of understanding that is
*incorrigible* by improvement of the subject's cognitive
condition or conceptual repertoire (see Bealer 2002: 104). So, if we
determinately understand a specific concept, we will have
truth-tracking intuitions (and therefore also truth-tracking *modal
intuitions*) about propositions in which this concept is involved.
For example, it is because one determinately understands the concepts
of a *square* and a *triangle*, that their intuition
that nothing can be both a square and a triangle is truth-tracking
and, thus, provides them with evidence that it is *impossible*
for something to be both a square and a triangle.



Christopher Peacocke (1999, 2002) explicitly puts forward an account
of modal knowledge that appeals to understanding and tacit knowledge
of certain modal principles, while it eschews the role of intuition.
Peacocke tackles the Integration Challenge and, in particular, the
fact that we lack a causal connection to modal facts and properties as
commonly understood in the metaphysical framework of possible worlds.
He believes that the best way to solve the problem is to adopt
Moderate Rationalism, which



> 
> 
> seeks to explain cases of *a priori* knowledge by appeal to the
> nature of the concepts that feature in contents that are known *a
> priori* (2004: 199).
> 
> 
> 



More precisely, Peacocke holds that understanding of metaphysical
modality, namely the concepts of possibility and necessity, consists
in having *implicit knowledge* of what he calls *Principles
of Possibility*, which include principles concerning the rules of
concept use, as well as constitutive (or essentialist) principles.
These principles govern understanding and evaluation of modal
discourse and accordingly are implicitly known and deployed by
subjects that correctly understand the modal concepts. Crucially, for
Peacocke, these principles are *necessary* truths, and
understanding and being able to deploy them is essential to modal
thinking and evaluation. As he puts it,



> 
> 
> we must be able to identify some of [these principles] if reasoning
> within the scope of counterfactual suppositions is to proceed. (1999:
> 173)
> 
> 
> 



Talk of a subject's *tacit knowledge* of the
Principles of Possibility might suggest that Peacocke's theory is
modelled on the way in which principles of grammaticality govern how
normal adult speakers understand and evaluate grammaticality in their
native language. Classic Chomskian theory holds that adult speakers
have some grasp or tacit knowledge of certain principles of grammar
governing correct expression and communication in our natural
language. However, Peacocke makes an important qualification to
the analogy with the Chomskian view. Although an ordinary thinker
might not be able to state the Principles of Possibility explicitly,
she will have *reasons* supporting her modal
judgements, i.e., some way of articulating the beliefs or conceptions
supporting her judgments of possibility and necessity. In this sense,
Principles of Possibility "bear a much closer relation to [one's]
personal-level modal thought than do the principles of grammar to his
thought about his own language" (1999: 164).



For a recent view that combines understanding of meaning and intuition
for knowledge of modality, see Boghossian Ch. 13 in Boghossian and
Williamson 2020.


#### Critical Questions for Intuition- and Understanding-Based Accounts



**The Causal Connection Question:** One might wonder
*how* intuition might justify beliefs about modal facts and
properties that we are not causally or spatio-temporally connected to.
How can intuition yield knowledge of modality if there is no causal
connection between possible worlds and minds? If there is no causal
connection between the mind and the modal fact, what kind of epistemic
connection could an intuition provide us with? (For discussion see
Bealer 2002).



**The Justification for Implicit Knowledge Question:**
Sonia Roca-Royes (2010) draws attention to the following problem in
Peacocke's epistemology of modality. On Peacocke's
account, it appears that our knowledge or understanding of modality is
parasitic on our knowledge of the Principles of Possibility, which are
the principles anyone who possesses the concept of possibility tacitly
knows. But how do we know such principles in the first place, or,
equivalently, how does one manage to possess the right
possibility-concept? We determine that something is possible or
necessary for an entity in part through our tacit knowledge of them,
which includes knowledge of what is constitutive of the entity, namely
what it is to be the kind of thing in question. As a consequence of
the relation between the role of constitutive principles and our
evaluation of specific modal claims for the purposes of generating
modal knowledge, a comprehensive account of modal knowledge is
incomplete without a picture of how we come to know the relevant
constitutive principles involved in our evaluations of modal
knowledge. Peacocke has taken up this challenge in recent work (2020).
More recently, Roca-Royes (2019) has generalized similar concerns to
any account of modal knowledge that rests on concept possession and
understanding.



**The Implicit to Explicit Knowledge Question:** We said
that for Peacocke our knowledge or understanding of modality is
parasitic on our knowledge of the Principles of Possibility. However,
it seems somewhat unclear *how* our tacit knowledge of
Principles of Possibility exactly gives us explicit knowledge of modal
facts. In other words, it seems that Peacocke owes us an answer to the
following question: How exactly are we to epistemically move from
(implicit) knowledge of Principles of Possibility to (explicit)
knowledge of modal facts or propositions so that knowledge is
transmitted? In answer to this question Peacocke offers the
following:



> 
> 
> If it is granted that implicit knowledge of the Principles of
> Possibility is appropriately employed in reaching modal judgement, we
> can see how the judgement so reached is knowledge. Provided that any
> non-modal principles upon which she relies are known, a
> thinker's modal judgements reached by the proper use of the
> implicit knowledge of the Principles of Possibility will, in the
> nature of the case, be knowledge. This is not only a matter of
> reliability. The judgement of the modal truth is explained by the
> thinker's implicit grasp of principles which make the modal
> truth hold. (1999: 162)
> 
> 
> 



However, this leaves open what it means exactly to appropriately
employ the Principles of Possibility. Finally, thinking of the debate
between internalism and externalism in epistemology, it is relevant to
ask whether our implicit knowledge of the Principles of Possibility
guides our judgment in a way such that this is *accessible* to
the subject.


## 5. Varieties of Essentialism



Essentialism has recently become a major area of investigation in the
epistemology of modality. Essentialist accounts of modal knowledge
draw on results from recent metaphysical debates about essence.
Generally, metaphysical
 essentialism
 is the thesis that, in addition to mere *accidental
properties*, entities also have *essential properties*.
Traditionally, essential properties have been analyzed as those that
*necessarily* belong to the objects that they pertain to. In
his influential (1994) article, however, Kit Fine has argued against
this analysis or reduction of essence to necessity. Fine provides
counterexamples to the traditional view by pointing out that there are
properties that an entity \(x\) has necessarily, though it is
plausible that they do not belong to the essence of \(x.\) The notion
of essence that Fine is working with is a broadly Aristotelian notion,
according to which the essence of an entity \(x\) is the *real
definition* of \(x\). Real definitions are contrasted against
nominal definitions. *Nominal* definitions define words that
stand for entities in the world, while *real* definitions
define entities themselves by telling us what is essential to them.
(Note that the explanation of essence in terms of real definition is
not intended to be a reductive one.) For example, the nominal
definition of "water" is, say, the drinkable liquid that
is found in rivers and lakes on Earth, while the real definition of
water is H2O. (Note that, besides Aristotle, this
*definitional* notion of essence is already present in
 Locke
 and
 Husserl.)



Most essentialist accounts in the epistemology of modality rely on
this Finean (or Neo-Aristotelian) notion of definitional essence. The
rejection of the traditional account of essence, according to which
essence reduces to necessity, paved the way for what can be called
*Finean Essentialism* (FE), a very influential view in the
metaphysics of modality.



(FE)
Metaphysically necessities are true in virtue of (or: are
 *grounded*
 in) essentialist truths.


Since our focus here is on essentialism as it is employed in the
*epistemology* of modality, we refer readers interested in
metaphysical issues concerning (FE) elsewhere. (For discussion in
favor of (FE), see Lowe 2008, 2012; Hale 2002, 2013, 2018; Kment 2014,
2021; Rosen 2015; Jago 2021; Tahko 2017, 2018; Wallner 2020; Wallner
& Vaidya 2020; and Wilsch 2017. For criticism, see Della Rocca
1996a,b; Gorman 2005; Zalta 2006; Correia 2007; Cowling 2013; Wildman
2013; and Livingstone-Banks 2017; as well as Leech 2018; Mackie
forthcoming; Noonan 2018; Romero 2019; Van Cleve 2018; and Wildman
2021.)



The core idea of essentialist accounts in the epistemology of modality
is that we acquire modal knowledge on the basis of *knowledge of
essence*. But note that
 (FE),
 i.e., the fact that essences *metaphysically ground* modality,
by no means *entails* that knowledge of modality must proceed
via knowledge of essence. Otherwise put, metaphysical priority
doesn't require epistemic priority. Nonetheless, on the basis of
(FE) essentialists identify knowledge of essence as one chief pathway
to modal knowledge.



One of the reasons for the growth of interest in essentialism in the
epistemology of modality stems from the criticism or incompleteness of
other accounts based on understanding, conceivability, or
counterfactual reasoning. An understanding-based theory such as
Peacocke's, for example, naturally integrates an essentialist
component by identifying the constitutive principles for modal
knowledge with essentialist principles. Likewise, theories of
conceivability such as Chalmers' and Yablo's, as well as
Williamson's counterfactual theory, have been criticized for
failing to take adequate account of the role of essences in the
acquisition of modal knowledge (e.g., Roca-Royes 2011a,b; Tahko 2012;
Vaidya & Wallner 2021).



The essentialist claim *that our modal knowledge depends on our
essentialist knowledge* raises two main questions:


1. How do we *gain* knowledge of essences in the
first place?
2. How do we *transition* from essentialist
knowledge to modal knowledge?



Following Fine, E.J. Lowe (2008, 2012) characterizes the essence of
\(x\) as the real definition of \(x\). Lowe's answer to
 (a)
 is thus straightforward: we know the essence of \(x\) simply by
*understanding what x is.* Unfortunately, Lowe does not
elaborate on his notion of *understanding* (see Tahko 2017,
2018 for discussion). Instead, he puts forward a transcendental
argument for the claim that we have knowledge of essence. According to
this,



> 
> 
> Knowing an entity's essence is simply knowing what that entity
> is. And at least in the case of *some* entities, we must be
> able to know *what they are*, because otherwise it would be
> hard to see how we could know anything at all about them. (Lowe 2012:
> 944; see Sgaravatti 2016 for criticism)
> 
> 
> 



Crucially, "*knowing what things are*" is meant to
capture knowledge of properties without which the object in question
would not be the thing it is. That is to say, Lowe does not talk about
mere contingent classifications (such as, say, *being a gift*
or *being located at the doorstep*) but essential properties
that figure in the real definition of a thing.



Bob Hale's (2013, 2021) answer to
 (a)
 is twofold. He distinguishes between *a priori* and *a
posteriori* knowledge of essence. In the case of *a priori*
knowledge of essence, essentialist knowledge is based on knowledge of
*meaning*. Hale acknowledges the difference between
*real* and *nominal definitions.* He then argues that
sometimes both a nominal and a real definition of an entity \(x\) can
be given by using the same words. For example, Hale argues that
knowing the nominal definition of the word "rectangle",
namely knowing the necessary and sufficient conditions for the
application of the word, suffices for knowing *a priori* the
real definition or essence of being a rectangle (i.e., *a
four-sided closed figure consisting of four right angles*).



Additionally, Hale maintains that even where there is no
*explicit* nominal definition for a word, like for example in
the case of basic logical constants, such as "and",



> 
> 
> knowing what [the word] "and" means is sufficient for
> knowledge of the essence of truth-functional conjunction. (Hale 2013:
> 258)
> 
> 
> 



So, for Hale we can gain knoweldge of essence *a priori* via
both implicit and explit knowledge of meaning.



On the other hand, with regard to *a posteriori* knowledge of
essence, Hale relies on a Kripke-style deduction model.



(H1)
If some \(x\) is \(F\), then it is essential to \(x\) that it is
\(F\).
(H2)
\(x\) is \(F\).
(H3)
Thus, it is essential to \(x\) that it is \(F\).


Of course, (H1) is not going to be true for all instances of \(x\) and
*F*. However, Hale thinks that one can come to know in an *a
priori* manner claims such as *if x is human, then it is
essential to x that it is human*. Similarly, we know that it is
*not* true that *if \(x\) is a musician, then it is
essential to \(x\) that she is a musician*. According to Hale,
this is done by distinguishing between *pure* and *impure
sortals* (2013: 270-275). So, for Hale, the major premise in
(H1) is known *a priori*. The minor premise in (H2) might be a
piece of *a posteriori* knowledge, such as, e.g., that Joanie
is a human. When (H2) is *a posteriori*, the conclusion (H3) is
also *a posteriori*, since the combination of an *a
priori* premise and an *a posteriori* premise always yields
an *a posteriori* conclusion.



In sum, Hale holds that knowledge of essences can be gained from
knowledge of meaning as well as from knowledge that is established via
empirical investigation. By contrast, for Lowe the source of knowledge
of essence is understanding, which is different from both knowledge of
meaning and empirical investigation. (Still, Lowe doesn't mean
to rule out that *a posteriori* knowledge may contribute to our
knowledge of essence, especially concerning kinds. See Tahko (2017,
2018) for discussion of Lowe's view concerning empirical
knowledge of essence.) Although Hale and Lowe's views on how we may
gain knowledge of essences differ, they agree on how knowledge of
essences can give us in turn modal knowledge, namely by deductive
inference. The argument is as follows:



(E1)
If it is essential to \(x\) that it is \(F\), then it is necessary
that \(x\) is F.
(E2)
It is essential to \(x\) that it is \(F\).
(E3)
Thus, it is necessary that \(x\) is \(F\).


As we saw, inferring
 (H3)
 from
 (H1)
 and
 (H2)
 yields knowledge of essence. Then, inferring (E3) from (E1) and (E2)
is to use knowledge of essence to gain knowledge of necessity.



Boris Kment (2021) puts forward an account of modal knowledge based on
his own modal metaphysics (2014). On Kment's metaphysical
framework, modal facts are partially grounded in what he calls
*metaphysical laws*, which also comprise *essentialist
truths*. Thereby, much of our modal knowledge for Kment depends on
knowledge of the metaphysical laws, including essentialist truths.
Kment discusses two ways in which we may acquire knowledge of such
laws (i.e., two ways to answer
 question (b)
 above). First, *abductively*, via inference to the best
explanation (IBE). Second, we may come to know the metaphysical laws
by relying on our *conceptual or linguistic competence*.



As to the first method, Kment holds that metaphysical laws (including
essentialist principles) play a crucial role in both metaphysical and
causal explanation. Accounting for what grounds or causes some
non-fundamental fact crucially involves making assumptions about
metaphysical laws. As for IBE, Kment holds that



> 
> 
> an abductive inference that establishes the account [of grounding or
> causation] will support these assumptions about metaphysical laws as
> well. (Kment 2021: S1969)
> 
> 
> 



For example, according to our best explanation, the fact that my cup
of coffee is hotter than your glass of iced tea is grounded in the
fact that the mean molecular kinetic energy of the former is higher
than that of the latter. Within Kment's framework, this account
entails that there is a certain metaphysical covering law that is
instantiated in this particular instance of grounding. In this case,
the law in question is the real definition or essence of
*being-hotter-than*: one object is hotter than another iff the
mean molecular kinetic energy of the former exceeds that of the
latter. In effect, for Kment, the epistemology of metaphysical
(essentialist) laws is a *byproduct* of the abductive
epistemology of grounding and causation.



As for the method of *conceptual competence*, Kment remarks
that competence with a term often requires (at least implicit)
knowledge of part or all of the *real definition* of the thing
picked out by the term. For Kment, real definitions are a type of
essentialist truths. To have competence in using the notions of
metaphysical necessity and possibility, one must know, at least
tacitly, that metaphysical modality is connected to metaphysical laws,
including laws that govern what is essential. (For a similar view, see
Peacocke 1999,
 SS4.3
 above. The role of linguistic competence in the acquisition of
essentialist knowledge has also been stressed by Hale 2013, 2021).



Thus, Kment's theory answers
 question (a)
 by appealing to IBE and conceptual competence. But what is his answer
to
 question (b),
 namely, how are essentialist knowledge and modal knowledge connected?
By contrast with Lowe and Hale, who appeal to deductive inference from
knowledge of essence to knowledge of necessity, Kment holds that
essentialist knowledge contributes to our modal knowledge by
restricting methods such as conceiving and counterfactual reasoning,
in other words, by providing *epistemic friction*, in the
terminology introduced above. His account, thus, indicates a possible
answer to (PMEF) (see
 SS2).



Mark Jago (2021) also offers an essentialist account of modal
knowledge. According to Jago, we can explain our knowledge of
metaphysical modality by way of our (implicit or explicit) knowledge
of essence. Like others, Jago aims to refute long-standing skepticism
against essences; to do so, he lays out a metaphysical account
according to which essences are simply bundles of located
properties:



> 
> 
> Essences are *constitutive* of material objects. Located
> properties "bundle" together to form a material object;
> and each property in the bundle is essential to the material object
> thereby constituted. Each material object is numerically identical to
> a located bundle of its essential properties. (Jago 2021: S1987; see
> also Barker & Jago 2017)
> 
> 
> 



Moreover, for Jago we can refer and single out these bundles
straightforwardly, in thought or language, by conceptualizing them
under kinds. According to Jago,



> 
> 
> there is a tendency linking (i) reference to a material object, (ii)
> our conceptualising that object under some kind \(F\), and (iii) our
> belief that that object is essentially \(F\). (2021: S1992)
> 
> 
> 



Notwithstanding some exceptions to this tendency, Jago takes it to be
appropriately reliable and safe from nearby error. On Jago's
*externalist* epistemology of essence, a belief constitutes
knowledge if it has an appropriate connection to reality. He takes
reliability and safety to constitute such an appropriate connection to
reality. Hence, Jago concludes that



> 
> 
> [w]hen one has a referent \(a\) in mind and conceptualises it under
> some kind \(F\), and thereby believes it to be essentially \(F\), that
> belief will often constitute knowledge that \(a\) is essentially
> \(F\). (Jago 2021: S1992)
> 
> 
> 



Knowledge of essence is thus secured by a reliable connection with
reality, which is due in part to the way we think about objects and
form beliefs about them. Knowledge of essence, in turn, leads us to
knowledge of necessity and possibility via a conceptual connection
between essence and necessity. For Jago, "it is a conceptual
truth that whatever is essentially \(F\) is necessarily \(F\)";
(2021: S1994) thereby, possessing the concepts of
"essence" and "necessity", together with the
relevant essentialist knowledge jointly results in knowledge of
necessity.



An account pairing essentialism with modal empiricism comes out of
Antonella Mallozzi's (2021a, 2021e) work. According to Mallozzi,
we can clarify what the normative constraints on good modal reasoning
are by appealing to essences. Specifically, she maintains that
essences are special core properties that have distinctive explanatory
powers in accounting for how things are--as she puts it, essences
are *superexplanatory*. Mallozzi focuses on examples involving
kinds and illustrates how essences typically cause and explain many
properties and behaviors that consistently co-occur in the instances
of kinds. For example, the atomic constitution of a chemical element,
say silver, explains why all samples of silver share a whole host of
properties, such as density, electrical and thermal conductivity,
disposition to combine chemically, and so on. Atomic number is, thus,
the essence or "nature" of silver, for Mallozzi, because
of its powerful role in explaining the properties shared by all
samples of silver. Accordingly, given
 (FE),
 silver necessarily has that atomic constitution. Against
long-standing skepticism against essences, Mallozzi emphasizes that
such superexplanatory one-to-many causal structures helps clarify in
what sense essences are held to constitute the "nature" of
things, as well as how we can know about them. (Godman, Mallozzi,
& Papineau 2020 further investigate the metaphysics of kinds in
terms of superexplanatory properties, particularly for biological
kinds.) Mallozzi gives a moderate empiricist answer to
 question (a)
 above. In most cases we acquire knowledge of essence empirically,
largely via scientific investigation aimed at discovering the relevant
causal and explanatory information. As to
 question (b),
 Mallozzi holds that once we have knowledge of essence, we may then
proceed to gain knowledge of metaphysical necessity inferentially, via
a fundamental Kripkean bridge-principle ("*If \(X\) is
essentially \(F\), then necessarily \(X\) is \(F\)*").



Vaidya (2010) has proposed an account of our knowledge of essence that
is influenced by Husserl's (1973) method of *eidetic
variation*, according to which we get access to the essence of an
object by varying its features in imagination. If a feature is seen to
be invariant, then it is an essence. In contrast to other
essentialists discussed here, Vaidya explicitly targets
*understanding* and not *knowledge* of essence.
(Following Kvanvig 2009, Vaidya takes understanding [but not
knowledge] to be compatible with epistemic luck.) Taking
Husserl's ideas only as a point of departure, Vaidya holds that
we can gain understanding of the essence of some object \(x\) by
varying properties of \(x\) in our imagination. Of those properties
that are invariant over the multiplicity of variations, we judge that
they are essential to \(x\). (See Wallner forthcoming for a discussion
of Husserl's epistemology of essence in contrast to that of Lowe
and Hale, and Michels (2020) for a critical discussion of Vaidya.)


### Critical Questions for Essentialism



**The Existence Question:** Some are skeptical that there
is a real distinction between accidental and essential properties.
Quine (1953 [1961], 1960) argued that whether or not a property is
essential to an object depends on how we refer to it. More recently,
Sidelle (1989) has provided an anti-realist view of essences. Mackie
(2006) and Asta (2008, 2010, 2013) have offered a critique of
realist approaches to essences. Further criticism of essences comes
from recent philosophy of science. Particularly, several philosophers
of biology have criticized biological essentialism (e.g., Ereshefsky
2010; Leslie 2013; Okasha 2002; for discussion: Devitt 2021; Dumsday
2012).



**The Metaphysics of Essence Question:** If knowledge of
modality depends on (or crucially involves) knowledge of essence, then
what essences are metaphysically influences any story about how we
know about essence and, hence, modality. Hence, the following
metaphysical questions concerning essences are crucial for the
epistemology of essence: What are essences? Are they the sum of the
essential properties of a given entity, or kind? Are essences distinct
entities from those things that they are essences of? Is (knowledge
of) essence linked to (knowledge of) *de dicto* or *de
re* necessity (or both)? Are there *individual essences*
which uniquely identify a certain entity or only general essences that
pertain to kinds of entities? Do all entities have exactly the same
kind of essence? For example, do social kinds have the same kind of
essence that natural kinds, or mathematical kinds have?



Nonetheless, on the basis of
 (FE)
 essentialists identify knowledge of essence as one chief pathway to
modal knowledge.



**The Transition Question:** A central question for
essentialism concerns the transition between knowledge of essence and
knowledge of modality (see
 question (b)
 above). For deduction theories that deploy the inference from
 (E1)
 and
 (E2)
 to
 (E3),
 one should ask: how is the bridge-principle connecting essence to
modality, (E1), known? Horvath (2014) argues that it isn't clear
how we come to know the bridge principle (E1). As Horvath remarks, a
(purportedly non-modal) real definition or essence-statement (like
"gold is *essentially* the element with the atomic number
79") doesn't make any explicit claim about metaphysical
possibility or necessity. Because of that, definitional essences do
not seem generally capable of explaining or grounding metaphysical
modality. As Mackie (forthcoming) puts it:



> 
> 
> It looks as if the account of essence in terms of real definition is
> intended to deliver a modal rabbit out of a non-modal hat. And I
> don't see how this can be done.
> 
> 
> 



Recently, however, Wallner and Vaidya (2020) have proposed a
*non-reductive* interpretation of Finean Essentialism,
according to which
 (E1)
 follows from the essence of essences in virtue of the fact that
essences have modal bearing. Essences via their modal bearing
constrain what is objectively necessary and possible for a given
entity. Hence, their view might provide an answer to this
question.



**The Language to Essence Question:** Some essentialist
accounts hold that knowledge of meaning or conceptual competence
importantly contributes to knowledge of essence (e.g., Hale's
and Kment's). This raises a more specific transition question
concerning how we get to knowledge of essence via linguistic or
conceptual competence. It might be argued that we acquire knowledge of
essence by *reflecting* on our conceptual-linguistic practices.
However, how could our conceptual or linguistic practices tell us what
are the essential natures of mind-independent things? Most theorists
appeal to *implicit* knowledge of essence. But what does this
mean, exactly? Particularly, how do we find out what we know
implicitly?



**The Completeness Question:** According to Hale's
epistemology of essence, we can come to know essentialist facts by
deducing them from essentialist principles (like in the inference from
 (H1)
 and
 (H2)
 to
 (H3)).
 However, one might ask whether knowledge of the essentialist
principle in (H1) is not itself already essentialist knowledge. In
other words, it might be questioned whether such an account of
essentialist knowledge can be complete (for discussion: Wallner
forthcoming). Wallner (forthcoming) also points out that in order for
us to successfully employ Hale's distinction between pure and
impure sortals that is supposed to differentiate essential from
inessential properties, we might have to presuppose essentialist
knowledge.


## 6. Perception



Traditionally, modal epistemologists have assumed that we cannot gain
knowledge of modality by investigating what is actually the case (see,
e.g., Craig 1985; Peacocke 1999). In particular, it seems that our
perceptual capacities *on their own* cannot yield knowledge of
what is possible and necessary. Perception, so the story goes, shows
us at best how things are, not how they could have been or must be. If
necessity is truth in *all possible worlds*, and perception
only provides us with evidence for how the actual world is, how can we
perceive necessity? Similarly, if non-actualized possibilities have no
truth-maker in the actual world, since they are non-actualized, how
can we perceive possibility? One might *infer* from how things
are that they might be a certain way, but how can one perceive how
things *merely could be*? In light of these considerations,
perception has been thought to be categorically inappropriate for
gaining modal knowledge. Recently, modal epistemologists have
challenged the traditional stance. In particular, some have switched
the focus of the epistemology of modality from far out claims about
the possibility of zombie worlds to every-day modal claims, such as
whether the couch could make it up the stairs, or that Joel can climb
the boulder.



Margot Strohminger (2015) uses practical examples of modal knowledge
to challenge the idea that we cannot perceive possibility. For
example, at least in some instances we seem to be able to *see*
that we *can* climb a tree (even if we have not yet climbed
it), or that we can reach a certain mug (even though we have not yet
tried). In Strohminger's view, one literally perceives the
possibility, rather than seeing something first and then making a
(possibly tacit) inference on the basis of what one sees. Importantly,
a defense of the pure perception of possibility requires a view of
perception where something more than low level properties, such as
color and shape, are present in perception. One class of views on
which perception provides more than just low-level properties are
affordance theories, due to Gibson (1979). On an affordance view, one
may hold that possibility is part of what we perceive. For example,
Iris sees that *the door knob can be turned*.



Barbara Vetter has recently expanded her work on the metaphysics of
potentiality (2015) and developed a perceptual account of modal
knowledge based on every-day cases and affordance views of perception
(see Gibson 1966; see also Nanay 2011, 2013). According to Vetter
(2021), we literally see potentialities or possibilities as part of
the content of our perception. In her (forthcoming) she emphasizes
that her account is *ambitious*. In her view, all of our modal
knowledge is based on knowledge of our own abilities and dispositions,
as well as the dispositions and affordances of objects around us.
Modal knowledge is, thus, for Vetter, distinctively empirical, in that
it requires experiencing such dispositions and affordances.



While Strohminger and Vetter focus on knowledge of non-actual
possibilities, Catherine Legg and James Franklin (2017) hold that one
can perceive *necessities* visually through certain kinds of
diagrams, such as picture proofs in mathematics. The diagrams
themselves provide us with a perceptual path to seeing that certain
kinds of truths are necessary (see also Legg 2012).


### Critical Questions for Perceptual Theories



**The Is-It-Really-Perception Question:** Does sensory
perceptual experience on its own really give knowledge of what is
possible or necessary, or does the knowledge use rational intuition
about the perceived content as well? If we literally see that
something is possible, what does its possibility look like? What is a
visual appearance of being possible?



**The Modal Kind Question:** What kind of modality does
one perceive? For example, when I see that I can reach a mug, what
kind of modality is it that I see? One view is that what I see is
practical possibility. And if that is so, this raises the
*Navigation question* of how one is to *epistemically
navigate* from practical possibility to metaphysical possibility.
Do we navigate from practical to metaphysical possibility by (tacit)
inference via the background assumption that whatever is practically
possible is also metaphysically possible? Or does this background
assumption inform our perceptual practices to the effect that we
indeed directly perceive metaphysical possibility?


## 7. Induction and Abduction



Sonia Roca-Royes and Bob Fischer both take a modest approach to the
epistemology of modality. Roca-Royes (2017, 2018) divides the space of
epistemological investigation via the ontological distinction between
concrete and abstract entities. In a 2017 work she offers a
similarity-based account of our knowledge of *de re* modality
for concrete entities. And in her (2018) she offers an account of
modal knowledge for abstract entities. Fischer (2017) divides the
space of epistemological investigation via a topical distinction
between *ordinary* and *extraordinary* claims.



Roca-Royes aims to answer the question: how can we come to know what
is possible for a particular entity? A starting point for her account
is the following example:



> 
> 
> I know that the wooden table in my office, Messy, is not broken. How
> do I know that? I see it. Although not broken, Messy can break. How do
> I know that? Because the table I had before Messy, which we may call
> "Twin-Messy", was a twin-sister of Messy, and it broke;
> and I know that Twin-Messy broke because I saw it. (Roca-Royes 2017:
> 226)
> 
> 
> 



Her account can be unfolded as follows:



(RR1)
\(S\) knows (via perception, say) that Twin-Messy actually
broke.
(RR2)
\(S\) knows that what is actual is possible.
(RR3)
*So, \(S\) can warrantedly transition to:* It is possible
that Twin-Messy breaks.
(RR4)
\(S\) knows that "objects similarly made out of the same
sort of materials are susceptible to similar effect" (2017:
227).
(RR5)
\(S\) knows that Messy is similarly made out of the same sort of
materials as Twin-Messy was made.
(RR6)
*So, \(S\) can warrantedly transition to:* It is possible
that Messy breaks.


Crucial to Roca-Royes's account is the notion of an
*epistemic counterpart*, whereby \(a\) is an epistemic
counterpart of \(b\) just in case there's a point in each of
\(a\)'s and \(b\)'s timelines where they are relevantly
similar (e.g., made from the same kind of materials) and, in virtue of
this, what has happened to *a informs* us of what could happen
to \(b\). In the example: Twin-Messy's breaking informs us that
Messy can break. Premise
 (RR4)
 plays a major role in Roca-Royes' account. She calls the
knowledge at stake here *nomic-like* (2017: 229) and clarifies
that it is supported *inductively*, since it heavily relies on
the uniformity of nature.



Fischer (2017) proposes a *Theory-Based Epistemology of
Modality*, TEM, for extraordinary or philosophical modal claims.
The basic idea is that we are justified in believing an extraordinary
modal claim, \(m\), only if we are justified in believing a theory
\(T\) from which \(m\) follows. For example, we are justified in
believing that mind-body dualism is metaphysically possible only if we
are justified in believing a theory \(T\) from which mind-body dualism
follows. Importantly, Fischer holds that *abductive* methods
for theory choice, such as using theoretical virtues like simplicity,
are central to being justified in believing a theory. If the theory
\(T\) from which one would be justified in believing that mind-body
dualism is metaphysically possible is *not* the simplest
theory, all else being equal, then one would *not* be justified
in believing it, and thus not be justified in believing that mind-body
dualism is metaphysically possible.



For other discussions involving abduction see Hanrahan (2017), who
discusses it in the case of imagination, Biggs (2011), who discusses
it in the context of conceivability, and Biggs and Wilson (2021), who
discuss it in relation to Carnap and anti-realism. Importantly, for
Wilson and Biggs abduction is an *a priori* enterprise.


### Critical Questions for Induction and Abduction



**The Relevant Similarity Question:** Generalizing
 (RR4)
 above, Roca-Royes speaks of relevant similarity of an object with its
counterpart. But what are the relevant respects of similarity, and how
do we know that? This seems to be the most crucial question in
Roca-Royes' account. Roca-Royes addresses the issue of relevant
and irrelevant similarity for the concrete cases she discusses in her
2017 work (like Messy and Twin-Messy). However, Roca-Royes concedes
that the details for the generalizability of these considerations
about relevant similarity are still to be worked out in full detail.
(For further critical discussion of Roca-Royes' account see
Prelevic 2015)



**The Priority Question:** Fischer's TEM makes it
seem that our justification for extraordinary modal claims always
comes by way of having a theory first. However, one might wonder if
sometimes we have justification for extraordinary modal claims prior
to building theories that would justify them. Consider the
following:


1. For Berkeley, it is inconceivable for a tree to exist unperceived
by anyone.
2. If \(p\) is inconceivable for \(S\), then \(S\) has justification
for believing that p is impossible.
3. So, Berkeley has justification for believing that it is impossible
for a tree to exist, or anything for that matter, unperceived by
anyone.
4. Idealism is the view that existence depends on perception.
*Esse est percipe*.
5. So, Berkeley has justification for idealism.



However, Fischer's TEM appears to hold that Berkeley must first
believe with justification Idealism, for him to believe that a tree
cannot exist unperceived by anyone. This result appears to contradict
how we sometimes use conceivability to gain justification in order to
believe a theory. (For further critical discussion of Fischer's
account, see Biggs 2017 and Wirling 2020).


## 8. Modalism and Normativism



Some authors have recently tried to solve the Integration and the
Reliability Challenge by rejecting well-established views in modal
metaphysics.



Otavio Bueno and Scott Shalkowski (2015) adopt
*modalism* about modality. They maintain that there is no
reductive analysis of modality in terms of non-modal facts or
properties. For arguably one cannot reduce the truth of "It is
possible that \(P\)" to "It is true in some world, \(w\),
that \(P\)" without wondering whether or not \(w\) itself is
possible or impossible. The epistemological task for Bueno and
Shalkowski is thus to provide an account of how we come to know modal
truths while accepting a primitivist view of modality. In this way,
Bueno and Shalkowski aim to meet the Integration Challenge.



Bueno and Shalkowski describe their account of our knowledge of
non-actual possibilities as follows:



> 
> 
> On our account, what grounds modal knowledge is ultimately our
> knowledge of the relevant modal properties of the objects under
> consideration. ... Suppose we are trying to determine whether we
> know that the table Hemingway used to write on in his Key West house
> would have broken had a 26,000-pound giant African bull elephant sat
> on it. ...On our account, we know that it would have broken
> simply by knowing the properties that such an elephant has and the
> properties the table has, modal in character as they already are.
> (2015: 680).
> 
> 
> 



The core idea is that in many cases we arrive at modal knowledge by
investigating the relevant properties and objects in question rather
than turning to some special epistemic capacity, such as being
conceivable. For example, one can know that it is possible for an
unbroken table to break because it is breakable. How do we come to
know this piece of ordinary modal knowledge? We do so on the basis of
our knowledge of wood, chemical bonds, and the physical relations the
table can find itself in, such as having a giant bull elephant sit on
it.



Amie Thomasson (2021) contends that we should reject a widespread
*descriptivist* picture of modality. According to
descriptivism, the primary function of modal discourse is to track and
describe modal facts and properties, which supposedly exist
independently of our expressive capacities and make true our modal
statements. Instead, according to Thomasson's *Modal
Normativism* (MN), modal discourse is distinctively
*normative*, in that it



> 
> 
> serves the function of expressing, teaching, conveying, or (re-)
> negotiating semantic rules (or their consequences) in particularly
> advantageous ways. (2021: S2087)
> 
> 
> 



Possibility and necessity are thus to be explained by reference to
semantic rules, not to some mind-independent modal reality. For
example, according to Thomasson, the fact that *necessarily, all
bachelors are unmarried* shouldn't be explained in terms of
some modal fact involving male humans that are bachelors; but rather
in terms of the rules for correct application of the terms
'bachelor' and 'unmarried'; particularly, the
rule that "One may only apply 'bachelor' where
'unmarried' may be applied". Once (MN) is in place,
for Thomasson we can then explain modal knowledge in a straightforward
way. Speakers who can use the semantic rules correctly show
*implicit* modal knowledge. Whereas, speakers have
*explicit* modal knowledge when they develop the ability to
explicitly convey in the object language and indicative mood the
semantic rules: in our example, when they are able to express:
"Necessarily, all bachelors are unmarried". Importantly,
for Thomasson, we can still talk about modal truth. From the sentence
"Necessarily, all bachelors are unmarried" we can infer
"'Necessarily, all bachelors are unmarried' *is
true*" by applying the (deflationist) equivalence schema
"\(\langle p \rangle\) is true iff \(p\)" (see Thomasson
2021).


### Critical Questions for Modalism and Normativism



**The Completeness Question:** On Bueno and
Shalkowski's view we arrive at knowledge of modal propositions
through knowledge of modal properties. But how do we gain knowledge of
modal properties in the first place? For Bueno and Shalkowski
properties are understood in a deflationary way, that is, they are not
characterized in terms of universals or abstract entities. They are
simply traits of objects. We know that the vase is fragile because it
is made out of glass and glass *can* be broken if struck. But
knowledge of the fact that glass can be broken is itself modal
knowledge. Hence, some knowledge of *modal* properties is yet
to be accounted for.



**The Scope Question and its Consequences:** One might
question whether Thomasson's Modal Normativism succeeds in
explaining knowledge of *metaphysical* modality, particularly
as opposed to *conceptual* modality or *epistemic
analyticity*. Arguably, mastering the semantic rules determining
the actual application conditions of, say, "water", and
possessing the relevant empirical information, won't suffice to
settle whether it is metaphysically possible for water to be XYZ or
contain carbon. As a consequence, because of its sole focus on
semantic rules, Modal Normativism might imply that classical
metaphysical debates in philosophy are merely a matter of verbal
disagreement and negotiation. While it is not clear whether this
constitutes a problem, in the eyes of the modal normativist, it does
raise an important point of disagreement. For example, are
participants in the debate on the mind-body problem really discussing
the nature of consciousness in relation to the physical body or are
they just renegotiating our rules for "mind",
"body", and "conscious" etc.? For some the
mind-body problem is not about the words "mind" and
"body" but about minds and bodies (for discussion, see
Mallozzi forthcoming b).