## 1. Biography



The main source of information about Shepherd's life is a family
memoir written by her daughter and published for private use
(Brandreath 1886). Shepherd was born on an estate near Edinburgh where
she lived until she married in 1808. We know she was taught Latin,
geography, mathematics, and history by a private tutor who also
discussed some philosophy (Brandreath 1886: 26). As a student, she
choose to write essays on metaphysics often faulting the logic of
Hume's atheistic writings and Priestly's Unitarianism
(Brandreath 1881: 28-9). Her published works were written after
her marriage. But in 1802, a controversy in Edinburgh made a lasting
impression on her. The incident prompted Thomas Brown to publish the
first of several tracts defending Hume against the charge of atheism
and advocating a universal constant conjunction account of cause and
effect. Shepherd mentions this in her first book as a sign of the
public's susceptibility to the pernicious influence of Hume and
a motive for her literary project. ERCE devotes a chapter to
objections to Brown's regularity theory of causes and another to
detailed critique of the empirical results regarding the cause of
sentience announced by William Lawrence, a physiologist who adopted
Hume's account of causation (on the latter, see Boyle 2021,
Paoletti 2011, LoLordo forthcoming).



In the early 1820s, Shepherd accompanied her husband to Cambridge
while he studied for a master's degree awarded in 1823. Although
there seems to be no record of the people she conversed with there, it
might well be that William Whewell, who held a university fellowship
at that time, was among them. The family history records that he used
one of her books as a text book. He was deeply interested in devising
a workable and productive method of empirical inquiry but it was not
until 1860 that he achieved his theory of induction (see the entry on
 William Whewell;
 on Shepherd's interest in shoring up scientific practice, see
McRobert 2002). Her daughter reports that he was a frequent guest of
the couple who resided in London. The Shepherds corresponded with
Charles Babbage, who wrote a treatise on computational mathematical
induction (Babbage, 1989). The couple's social circle included
men and women of science, literary figures, and others of intellectual
accomplishment. She was known for her unanswerable logic and passion
for abstract metaphysical reasoning.



In addition to works mentioned above, Shepherd published three
articles: critical remarks on the metaphysics of John Fearn, a retired
naval officer (Shepherd 1828a), a very effective reply to
Fearn's counter-critique of her metaphysics (Shepherd 1832), and
an article on the single and erect object of vision (Shepherd 1827b).
In the present article, we focus on her two main philosophical
 works.[1]



The merits of her work were publicly acknowledged in several ways.
There is good evidence that one of her monographs was used as a
textbook at Cambridge. Her part of a sharp philosophical dispute was
published in a monthly magazine. Her theory of mind and self are the
subject of an entry in Robert Blakey's multi-volume *History
of the Philosophy of Mind* (1850). After her death and before its
recent recovery, her philosophy dropped from view for reasons that are
not entirely clear (Atherton 2005; Paoletti 2011).


## 2. Doctrine of Cause and Effect


### 2.1 Everything that begins to exist must have a cause



Shepherd's account of causality is advertised as contrary to
David Hume's in point of metaphysics, psychology, and
epistemology. Where Hume holds that common causal beliefs are due to
repetitious experience and acquired habits of imagination, she urges
they are caused and justified by perception and reasoning. Where Hume
holds that abstract ideas are impossible, Shepherd insists that
science and philosophical analysis are impossible without abstraction.
Against Hume, she argues that an uncaused change in the course of
nature is impossible and produces a proof that everything that begins
to exist must have a cause. According to her, the proof articulates a
line of reasoning the human mind is disposed to use, implicitly or
explicitly, in forming causal beliefs, attaining knowledge of causal
principles. and perceiving particular instances of them (e.g. EPEU
[2020: 314-316; Fantl 2016: 88). Incipient notions of causal
power and necessary connection arise as children form their earliest
beliefs about sensible objects (e.g. EPEU: [2020: 314-24]).



It would not be correct to say this begs the question against Hume.
She has several reasons for rejecting his views on the relation of
cause and effect. Perhaps the two most fundamental are the
impoverishment of a theory of mind that limits what we can apprehend
to sensory and reflective impressions and things that resemble them,
and the assumption that our ability to separate the idea of a cause
from that of an effect in imagination shows the ideas are separable in
nature and experience (Bolton 2010: 244-6; 2019: 132-38;
Landy 2020b). Her theory of causality and causal induction are
expounded in ERCE; her account of the cause and justification of
belief in the external world is developed in EPEU. This section is
mainly concerned with the former.



The first metaphysical tenet is the causal principle: it is necessary
that a thing that begins to exist has a cause (hereafter
"CP"). The argument for this begins with a clarification.
The notion of an effect is semantically tied to that of a cause. To
avoid this implication, Shepherd characterizes an effect as a thing
that begins to exist; so clearly stated, the question is whether
"a thing that begins to exist owes its existence to a
cause" (ERCE [2020: 34). She proposes a thought experiment.
Imagine an object different in nature from all objects we know except
for the capacity for its existence, that is, the ground of the
possibility of its existing when it does not yet exist. Suppose the
universe is an utter blank; nothing exists.With this understood, she
argues, it is impossible for the thing to begin to exist. This is
because its beginning to exist "cannot appear but as a capacity
some nature hath to alter the presupposed nonentity and to act for
itself whilst it is not in being." (ERCE [2020: 36). One way to
understand the reductive argument is this: (a) the beginning of
*x* must be an act; (b) the act must be the property of an
object which exists and has the capacity to actualize x; (c)
*x* does not yet exist; (d) nothing exists (supposition); so
*x* cannot begin to exist. This is valid but premises (a) and
(b) seem to assume what the argument is supposed to prove (Bolton
2017; Fantl (2016: 98) also finds the argument circular). However,
Rickless (forthcoming) is among those who object to this charge; he
argues it is doubtful the pair of premises means the same thing as the
conclusion. Arguably, though, Shepherd assumes it does. She assumes
that her idea of what is needed to begin *x* specifies a state
of affairs that satisfies her (controversial) idea of a cause. Nothing
shows that this is a fact about the world.



Jennifer Wilson (forthcoming) interprets the argument as an effort to
articulate the metaphysical reasoning behind the intuition that
nothing comes from nothing. Like Shepherd, she stresses that anything
that begins to exist must have a beginning: a transition from the
non-existence to the existence of the entity in view. Wilson notes
that this act, or event, need not be the property of an object, but
there must be one or more things that perform it. This is said to
explain the intuition because it is independently plausible,
metaphysically possible, and no worse off epistemically than the
alternative, This is consistent with the interpretation just offered,
but focused on a different issue: the need to connect non-being and
being in direct opposition to Hume's principle of the
separability of all things that are different, by contrast with the
modal notions of metaphysical possibility and actuality,



Rickless (forthcoming) takes the main task of Shepherd's
argument to be refuting the opinion that a thing's beginning is
other than its not existing at one moment and existing at the next.
(Hume asserts something like this but in terms of contraries
"non-existent" and "existent" (T [2000:
1.3.3.3])). Shepherd claims a thing begins only if there is something
that acts to begin it. Rickless suggests the strongest case that can
be made for this is illustrated by the fact that verbs such as
"to walk", "to sing", and "to
campaign" signify acts or activities that begin only if a
subject starts to do them; e.g., a walk begins if an ambient being
starts to walk, and not otherwise. The generalization of this pattern
is the implicit premise of the argument as Rickless interprets it, One
might object that an agent that single handedly begins to do an
activity is not a cause by Shepherd's definition, so this
argument may not prove anything she wants to hold. Rickless goes on to
make an important point about Shepherd's argument: it treats
"exists" as a predicate. This makes it vulnerable to
Hume's doctrine that the idea of existence is the same as the
idea of the object that exists; to think of an object is to think of
it as existent (T [2000: 1.2.8.4]). So even though Shepherd's
argument, as Rickless understands it, is cogent, Hume has ground on
which to resist it (as does Kant). This is true, but she has a case
to make. Shepherd respects Hume's preference for
"non-existent" rather than "not in existence" (see ERCE [2000:
37-8]). But she herself holds we have ideas of existence that
are modally and temporally qualified and explicitly argues that we
have a general idea of existence (EPEU [2020: 82-6]).



All derivations of the argument for CP found in the texts have
premises formulated in the terminology of the theory of cause and
effect Shepherd promotes. Most of them refer to things that begin to
exist as "qualities" of "objects." According
to Shepherd's list of non-Humean definitions: a cause is
"such an action of an object, as shall enable it, in conjunction
with another, to form a new nature, capable of exhibiting qualities
varying from those of either object in separation from the other. This
is really to be a producer of new being" (ERCE [2000: 63]). An
effect is defined as "the produced quality exhibited to the
senses, as the essential property of natures so conjoined." An
object is defined as "a combined mass of qualities; the result
of proportional unknown circumstances in nature, meeting with the
human senses" (ERCE [2000: 64]). According to these definitions,
we can say a cause is part of a configuration comprising: first, the
antecedent existence of two or more objects that taken together ground
the possibility of the existence of some quality Q when it does not
yet exist; second, the two objects' uniting and thereby forming
a new object that is the cause of newly existent Q; and third, the
object's being perceived with Q as its essential property.



A distinctive, perhaps unique, feature of Shepherd's metaphysics
is that the objects we believe to exist in the world are partly in us
(mind dependent) and partly unknown, exterior to, and independent of
minds and sensory organs. Objects, for her, are objects as we perceive
them; they are not fully formed unless perceived (see e.g. EPEU [2020:
72-3, 93]). That is, sensible qualities such as figures and
colors are not external properties of mind independent objects (as
e.g. Locke wants to say), nor sensations existing only in minds (as
Berkeley maintains), but relations that span the mind and scarcely
known entities outside the mind. She faults Berkeley for holding that
sensible objects are only ideas, not for holding that they are ideas
(e.g. EPEU [2020; 195-213]). (Atherton1996 and Rickless 2018
disagree about whether Shepherd misunderstands Berkeley's
idealism.)



In regard to ontology, the preexisting entities that ground the
possibility of the existence of so far non-existent qualities are
regularly called "objects", "natures",
"masses of qualities", or "unknown circumstances in
nature;" occasionally, they are designated by other terms (e.g.
"substance" (ERCE [2000: 53; EPEU [2020: 388)). Also,
"power" is synonymous with "efficient cause, or
productive principle;" it stands for "the property that
lies in the secret nature of objects, when unobserved by the senses,
and which determines the qualities that can be exhibited to them upon
every new conjunction" (ERCE [2000: 63-4]). Jeremy Fantl
(2016) takes this to suggest an ontology in which objects are bundles
of qualities, powers are basic (unreduced), and qualities are
individuated by the causal powers contributed by these qualities. If
this is right, it is natural to assume that objects are individuated
by their causal powers or the qualities their powers determine (Fantl
proposes the former). Shepherd does not use the term
"individuate", but relies on the notion of properties that are
essential to individuals (see especially ERCE [2000; 48, 57, 63; EPEU
[2020; 242, 243-3]). (Fields (forthcoming) argues that Shepherd
does not have a bundle theory.)



The secondary literature has little to say about Shepherd's
essentialism but there are many indications that it is heavily
influenced by a doctrine of Locke: "Essence may be taken for the
very being of anything, whereby it is what it is. And thus the real
internal, but generally in Substances, unknown Constitutions of
Things, whereon their discoverable Qualities Depend, may be called
their Essence" (E [1975: 3.3.15]); this motivates Locke's
distinction between real and nominal essences of kinds). LoLordo
(2200: 5-9) brings out Shepherd's interest in downplaying
Locke's worry that the observable qualities of individual bodies
fail to display divisions that might be regarded as delineating inner
constitutions; she also argues that Shepherd regards herself as the
true heir of Locke's legacy. Beyond that, however, her
metaphysical system seems to have been inspired, at least in part, by
Locke's notion of essence. Shepherd is convinced that the
patterns of change we observe among sensible objects manifest what
they essentially are, namely causes that essentially produce the
effects they do (e.g. ERCE [2000: 43-5, 47-9]). For
instance, "Fire ... must of necessity burn as much as it
must be red, otherwise the red object were not fire" (ERCE
[2000: 54]). It is true that some similar passages add that the stuff
would not be properly called "fire" but this is because it
would not be fire. Shepherd expresses the modal demand an essence
makes on an object by the term "obligation" and uses it to
define what Hume calls "necessary connection" of cause and
effect (ERCE [2000; 63]). This strongly suggests the necessity she
ascribes to causality is an expression of her essentialism.



The synchrony of cause and effect follows from the non-Humean
definitions of cause, effect, object, and power. The union of two
antecedently separate objects forms a new mass of qualities that
includes at least one quality that did not previously exist. The newly
formed mass is the mass that includes the novel quality. The new
object does not exist until the union is complete. As Shepherd puts
it, "[I]n their union, there exists those newly formed objects,
or masses of qualities called Effects, ... for in this union
Cause and Effect are synchronous, and they are but different words for
the same Essence" (ERCE [2000: 57]). As interpreted here, the
newly formed object and newly formed quality have synchronous
existence: one exists at a time if and only if the other does.



David Landy (2020a) offers a different interpretation of the argument
for synchrony which he uses to construct a defense against
Hume's contention that if causes and effects were
contemporaneous, then all objects would exist at the same time (see T
[2000: 1.3.2.7]). On this reading, if a quality begins to exist, the
transition from two separate objects to one unified object passes
through a "vanishingly short instant" in which the
antecedents and their union overlap and "all three must exist
synchronically" (Landy 2020a: 4). This is problematic because
synchrony for a moment is too brief for the relation between an object
and one of its essential qualities (compare Landy 2020a: 4, note 8).
We might also mention that if the separate antecedents and the unified
object literally existed at the same time, the union of antecedents
would be complete and incomplete at that time (see ERCE [2000:
50]).


### 2.2 Similar causes must have similar effects



Shepherd propounds a second causal maxim which we can call the
"Causal Similarity Principle" (hereafter
"CSP"): similar causes must have similar effects (ERCE
[2000: 43-9, 53-5]). Some scholars assume CSP and CP are
on an epistemic par, both known a priori on the basis of nothing but
Shepherd's concept of causality (LoLordo 2019: 11; Bolton 2019:
149). This has prompted the objection that CSP does not solve
Hume's epistemic problem. He asks for the necessary connection
between things such as smoke and fire which have been regularly
conjoined in experience: what entitles us to infer other cases will be
the same? To reply that CSP is a general conceptual truth is
empty--as if to say, otherwise the instances in question would
not be the same (see Ott 2011, quoted and glossed by LoLordo 2019).
There seems to be a disqualifying objection to this: CSP is not an a
priori truth based on nothing but concepts. It is derived from CP but
in conjunction with an a posteriori premise with existential
import.



Before we look at this, it is worth mention that Tanner (2022)
suggests that although Shepherd's causal metaphysics implies that
nature is uniform, i.e. things in the same kind must have similar
effects, in the absence of a reason to believe the metaphysical
theory, she offers nothing that answers Hume's demand to be shown a
reason to believe the similarity thesis.This weakness is overcome,
Tanner suggests, if the causal metaphysics is conjoined with a
principle of parsimony that governs the number of natural kinds we
should recognize, The conjunction is not the sort of reason Hume has
in view, but it is a rational justification for belief of the
similarity thesis. This may be true, but there is textual evidence
that the causal principles themselves are epistemically founded on
perceptual knowledge of the world (see below in this section and the
next)..

 The argument for CSP is made in several ways, but all of
them have two parts. One reviews the circumstances in which we come to
believe there is a particular cause when observing that a quality
begins to exist. This introduces a premise with modal and referential
features that set her account of causal beliefs apart from
Hume's. The second part offers Shepherd's reflection on an
object similar to one we believe to cause a certain quality to begin
its existence: if the two are in similar circumstance, what effects
can the duplicate have in view of CP? The upshot is that the
derivation of CSP has a premise that limits its scope to objects that
exist,


One derivation of CSP argues, *contra* Hume, that when we first
perceive some kind of thing, we may very well discover something about
its cause by "reasoning on an experiment" (ERCE [2000:
45]). When we are aware that some quality begins to exist and believe
it has a particular cause, we typically observe qualities of objects
that are present shortly before it appears. In favorable
circumstances, there are two and only two discernible objects which
coalesce at the moment the new quality begins to exist. For example,
if you pour vinegar into milk and see that it immediately breaks into
curds and whey, you are likely to believe the mixture of the two was
the cause of newly curdled
 milk.[2]
 The second part of the derivation is a reflection on two similar
liquids mixed in the same way. Shepherd argues that if the second did
not have the same effect as the first, then either something caused an
alteration in the second, so they are not the same, or it caused an
alteration in itself, which is impossible according to CP (ERCE [2000:
45, 46, 48-9]). We should ask why this matters given that the
proposition just asserted is circular and without extensional
import.



In another derivation of CSP, the first part invokes definitions that
accrue to particular objects that we believe to cause specific
effects: "If then an existence now in being, conjoined with any
other, forms thereby a new nature, capable of exhibiting new
qualities, these new qualities must enter into the definition of the
objects; they become part of their natures" (ERCE [2000: 47]).
Compiled from the experiences that inform us of the existence of
particular causes, such definitions report the sensible qualities and
other circumstances observed just prior to the novel appearance of one
or more qualities and record the observed effects of the newly formed
object. Provided the antecedently observed sensible qualities are
probable indicators of the kinds of previously existing objects
from which the new object results, a definition specifies two markers
of the kind to which the new object belongs. We can call on them in
collecting evidence that two objects are similar and predicting their
effects under various circumstances. This is the case whether or
not any of the antecedent natures (powers) are included in the
constitution of the newly formed nature (see ERCE [2000: 189]). So the
definition of an object purports to pick out all and only objects that
are exactly alike in respect of the powers they amass. (To be clear,
the subjects of definitions are particular objects; the definition of
a particular object is the definition of the natural kind to which it
belongs if kinds are individuated by causal powers; see section 2.1,
Fantl 2016),)



That CSP is made true by the constituents of actual objects is also
shown by the reflection that completes this derivation. Shepherd
argues that elicited objects are determined as composites: e.g. when a
fire is elicited from the juncture of two other objects, the
"combined qualities" that begin to exist are "the
whole qualities that fire, in every circumstance is capable of
producing" (ERCE [2000: 49,
 54]).[3]
 The truth of CSP is founded on the doctrine that the method of its
formation fixes the constitution of the resulting object, so similar
formative origins determine similar constitutions. Rounding the
derivation out: so on another occasion, the same pre-conditions are
"necessarily compelled" to be attended with the same
effects, or combined qualities: otherwise there would be the
"beginnings of existence by themselves" (ERCE [2000 49,
47-48, 52-55]). Although the circular maxim has a part
here, it is not what makes CSP true.



Definitions of objects are used to rebuff Hume's contention that
the course of nature can change spontaneously, without a cause that
alters it. She argues against his examples. He claims it is possible
that a body otherwise like snow should burn the skin and taste salty;
again, fruit trees that have regularly borne fruit in warm weather may
someday be productive in freezing cold. Shepherd counters that
although the stuff otherwise like snow may well be possible, it would
not be snow; rather than marking a change in natures' course, it
would be a different object with qualities arising from different
circumstances depending on nature's course. Again, "once
the proof has been afforded" that the nature of fruit trees
requires warmth if they are to grow and flower, it must be considered
impossible for them to have qualities "not originally in their
natures" (ERCE [2000; 81]).



At bottom, Shepherd's causal metaphysics rests on the intuition
that the formation of an object renders it what it is. It applies also
in mathematics (EPEU [2020:: 279]). Shepherd takes mathematical
objects to be particular things constructed by placing physical items
in spatial relations or relations understood to be arithmetical. Their
properties are known by inspection, comparison, and the like:
"my whole notion of the relation of cause and effect is aptly
imagined by the nature of the necessary results, included in the
juxtaposition of quantities" (EPEU [2020: 282]). Shepherd holds
that the general truths of natural science for which we have empirical
evidence are necessary and the necessary truths of arithmetic and
geometry are believed partly on the basis of experience (Bolton 2019:
149-52; LoLordo 2019: 11).


### 2.3 Definitions and other a posteriori necessary truths



Definitions of objects have attracted attention for several reasons.
One is that they. are holistic in the minimal sense that any given
kind of object is defined in terms of other kinds of objects or
qualities. For instance, fire can be defined as the object elicited by
concussion of flint and steel, and flint can be defined as the object
that, combined with steel, gives rise to fire. Some scholars worry
that Shepherd's definitions of natural kinds form a closed
system that is impervious to refutation and seek a solution to the
problem. It seems those who have this worry assume the
definitions in question are descriptive and to some extent formed
without empirical guidance--Locke's nominal essences in
effect, As interpreted here, however, the definitions Shepherd has in
view are formed on the basis of experience; they state the essential
properties of actual objects. She may think the meanings of names of
kinds in a natural language are based on them.



Definitions have also attracted attention because they are a
posteriori necessary truths. Kant has an account of how we can know
such truths, but Shepherd does not follow him in distinguishing
analytic and synthetic judgments (LoLordo 2019: 10, note 25). She does
not address this issue in the direct sort of way we might expect. The
issue for her is how we acquire knowledge and belief of the existence
of the external world and the causal principles that are its
foundations. It turns out that this is knowledge of roughly the sort
Kant found he needed to explain. Perceptual knowledge is the topic of
section 3.1.


## 3. Knowledge of the existence of an external world


### 3.1 Perceptual knowledge and reason



There is considerable evidence that Shepherd has a foundational theory
of perceptual knowledge, e.g. "Reason does establish this
beautiful and certain proposition, which is the foundation of all our
knowledge--That like causes must ever produce like Effects"
(ERCE [2000: 143-4]). The principles of the theory of causation
"regulate every opinion speculative and practical" (EPEU
[2020: xiii, 190]). The epistemic foundations of our knowledge
are the basic causal principles. Because knowledge of causal
principles is secured somehow by reason, she wants to suggest, they
are less subject to doubt than those offered by Hume (EPEU
[2020: 27-8]). Yet the most sharply focused issue about
Shepherd's epistemology discussed in the literature is the part
reason plays in knowledge.



As we saw, Shepherd holds we have an idea of a cause adequate for an
argument for CP. Fantl (2016) and Bolton (2019) assume this is an
example of knowing a principle by reason. But this is difficult to
make out. Fantl interprets the argument as a thought experiment
supposed to reduce the denial of CP to a contradiction, but finds no
unproblematic way to state the argument. Bolton interprets it as a
valid, but circular, argument which implies nothing about what happens
in the world.



Folescu (2020) objects to these accounts mainly because they take the
argument to confer knowledge. She finds the view that CP is a
foundational principle, i.e. a proposition known without basis in
knowledge of another proposition, to be in tension with the view that
CP is established by an argument. As Folescu understands it, the
argument for CP is analytic yet we are said to know the principle; she
concludes it is known without proof. This is confirmed by the fact
that shortly after stating this argument, Shepherd asks readers to
grant the causal principle so she can use it in making her points
against Hume (ERCE [2000: 39]; EPEU [2020: 164, note 9]). So, Folescu
maintains, although Shepherd sometimes seems to say causal principles
can be demonstrated, she ought not to (e.g. Folescu: 13-14). To
my mind, this is right and helpful.



Then what does reason contribute to our knowledge of the existence of
the external world? As Folescu interprets it, reason constructs
arguments which have a role similar to that of proofs in the practice
of early twentieth century mathematicians who built axiomatic theories
about neglected subjects such as sets. She provides an instructive
picture of their use of proofs to motivate acceptance of certain
propositions as axioms by bringing out the benefits it brings, e.g.
adopting an axiom may greatly increase the usefulness of the theory
(Folescu 17-19 ). But our interest is in Shepherd's
account of knowledge of foundational principles, or first principles.
Folescu quotes a neglected passage which states that first principles
are a sort of perception: "First principles are the perceptions
of the corollaries, inclusions, or necessary relations of our simple
impressions, and infants who have not a capacity fitted to generate
such perceptions are born idiots" (EPEU [2020: 314], quoted in
Folescu (2020: 11). Taking this to say first principles are
known without proof and characterizing this as a sort of intuitive
knowledge, Folescu mentions two sources known to Shepherd that might
have influenced her: Locke and Reid. Locke contrasts
intuitive and demonstrative knowledge. Briefly put, he holds we know a
proposition by intuition just in case when we join two ideas in accord
with a proposition-making relation, we perceive relations among the
combined representations which are sufficient to show the proposition
is true; we have demonstrative knowledge if the truth is perceived
only with aid of intuitive perception of intermediary truths (E [1975:
4.2.1-3; 4.7.1]). We might say, intuition presents us with
representational evidence of truth. According to Reid's doctrine
that we have intuitive knowledge of the principles of common sense, a
proposition known by intuition is believed as soon as it is
understood; it is known without seeking evidence or inferring it from
something else; knowledge of a principle is "the work of nature,
and our original powers." (EPI [2002: 452: quoted by Folescu
(2020: 12). According to Reid, intuitive knowledge is self evident in
that it neither has nor needs evidence of the proposition's
truth.



Folescu argues that Shepherd's position has more in common with
Reid's theory than Locke's. She notes that Reid recognizes
the utility of arguments about epistemically basic principles that
bring out the advantages of endorsing them as axioms; in this
connection, he explicitly mentions *reductio* proofs. She
suggests Shepherd intends CP to make the fundamental principle
accessible to reasoning and to bring out its self-evident truth.
Folescu admits Shepherd is critical of Reid's appeal to human
nature or instinct to explain the foundations of knowledge. But,
Folescu explains, Shepherd misses the point that Reid's theory
is not unlike her own. On this interpretation, Shepherd maintains that
first principles are known by intuition in the manner of Reid and she
recognizes that psychological explanations of belief of first
principles are useful for the general advancement of knowledge,



This brief summary does not do justice to the sophistication and
subtlety of Folescu's discussion of the interplay of psychology
and epistemology in Shepherd's thought. But the interpretation
is open to the objection that Shepherd's critique of Reid is
squarely addressed to the doctrine he holds, and on many occasions.
For instance, Reid "cuts the knot instead of untying it"
by referring belief in the existence of body to a natural instinct.
This is because it offers no satisfactory reason for belief or detail
about how it arises ([EPEU [2020: 5, 111-12]). Shepherd
propounds a more complex account:



> 
> The class of ideas which Dr. Reid terms instinctive ... I
> consider to be the conclusions of a latent reasoning: as the mere
> results and corollaries, included in the relation of those ideas and
> sensations already existing in the mind, and which were previously
> formed by the senses. (EPEU [2020: 170])
> 



 As she sees it, perception is not a primitive inexplicable
disposition; but it is "no more than an *observation of the
simplest relations of our ideas*--It is but a simple
*inference of the understanding*..." (EPEU [2020:
113, 3, 8]) This and other texts strongly suggest that reason confers
knowledge because it is the ability to grasp a relation between ground
and consequent. Yet reason is the means by which we perceive the
existence of external objects. Although Folescu's reading neatly
resolves a tension between the foundational status of CP and view that
we know the principle by means of an argument, it can also be seen as
opening the way for an alternative resolution, namely, that Shepherd
recognizes more than one basis on which reason can respond to an
epistemic relation between ground and consequent and rests causal and
perceptual knowledge on one of them.



Before saying more about this, we should get clear about what Shepherd
means by "perception." She explicitly disagrees with
Reid's theory that sensations always precede acts of perception
but are entirely extrinsic to them; for him, sensations are
intentional blanks that merely trigger the mind's formation of
the concept of an object and firm belief in its existence. By
contrast, when she uses the word "perception" it is
"in the sense of 'a consciousness of sensation', a
SENSATION TAKEN NOTICE OF BY THE MIND" ([EPEU [2020:
6-9]).



The continuation of one of Shepherd's objections to Reid
partially quoted above is more forthcoming. The gist is that
perception is "*the observation of the simplest relations of
our ideas"*; this is analyzed as "a simple inference
of the understanding;" this is broken down to "the
perception of the CONSCIOUS SENSE (which takes notice when it is
affected)" together with "the perception of THE
UNDERSTANDING" to the effect that the sense organs and mind must
be affected by objects external to both. Shepherd adds: "this
inference ... is knowledge rather than instinct" (EPEU
[2020: 113]).



This is no more than a sketch, but three things are clear. First, we
have two types of perceptual knowledge: consciousness of juxtaposed
sensations and understanding that some sensations are caused by
particular objects distinct from the amassed sensations. Second, the
relations discovered by understanding are inferred from
the--presumably temporal--relations of juxtaposition
perceived by consciousness; i.e. the order among a mass of sensations
known by consciousness provides some sort of basis from which
understanding infers the existence of a particular object that causes
certain sensations. (See especially the objection to Brown's
theory of instinctive belief (ERCE [2000: 138, 146]).) Third, if two
or more sensations are juxtaposed in consciousness, their relation is
part of a more comprehensive relation between items of consciousness
and objects unavailable to consciousness which is the locus of the
causal relation (see the dichotomy of inner and outer existences,
section 3.2). An interpretation on which reason confers perceptual
knowledge because it is inferential has considerable textual
support.



It is clear, Shepherd holds we can, and sometimes do, deliberately
argue from observed relations among things we perceive by sense to
conclusions about relations among the (unknown) objects that cause
them. She holds that although sensations are essentially felt and can
be essentially like nothing but sensations, they have non-essential
relations to other things, such as variety, sameness, contrariety, and
proportionality. She argues that there must be relations among
sensible quality sensations accumulated in experience that are similar
to relations among their respective causes. This is because if the
sensory system and the mind are functioning well, they always operate
in the same way, so the differences among temporally ordered
sensations must be due to corresponding differences among their causes
taken in the same order (EPEU [2020: 4749, 63-165,
703-704]). Not that the corresponding relations must be exactly
the same, but the same in some respect. Shepherd likens this to the
London diorama, an elaborate three dimensional walk-in illusion of the
city famous in her day; she often makes an analogy with algebraic
signs used to calculate the values of their significations under an
interpretation, and sometimes a language that needs
interpretation (e.g. Boyle, 2020: 100),


### 3.2 Psychology of belief in the external world



"All we know must be by means of *consciousness*, or
*sensations*," according to Shepherd (EPEU [2020: 7]). In
her usage, "sensation" is a general term for everything of
which a sentient being is conscious (EPEU [2020: 6,
133-60]). There are two classes of sensations: those that are
sensible qualities (colors, figures, etc.) and sensations of ideas.
Sensations that are sensible qualities are always caused in part by
the use of organs of sense and attended by sensations caused by using
them. They have an "immediate incontrovertible evidence" (EPEU
[2020:142, 700]). Ideas, but not sensations of them, refer to things
distinct from sensations. Strictly speaking, an idea is "the
result of that reasoning or observation which shows that there must
needs to an existence when we cannot perceive it" (EPEU [2020:
133-4]).



Shepherd undertakes to explain three common beliefs about the objects
of perception: their existence is continued, outside the mind, and
mind-independent. What is to be explained is how sensations can lead
to these beliefs about objects in view of the discrepancy between what
we know about the former and the properties we ascribe to the latter.
The first issue is: "Whence we know of any continued existence,
when we can immediately know nothing but our sensations" (EPEU
[2020; 20]). Sensations are interrupted, for example, by dreamless
sleep and by their constantly arising, perishing, and being replaced.
Her general procedure is to argue that sensations we acquire in
experience display various patterns that must have causes with the
properties just mentioned. The aim is to show that reasoning provides
reasons, or motives. for holding the common beliefs. The reasons may
not have propositional form and they have various degrees of
perspicuity, but all mentally competent human beings, regardless of
age, are conscious of them e.g. EPEU: [2020: 16-17, 71, 106)].
Because Shepherd gives minds to all sentient organisms, they too are
said to be conscious of reasons to believe the things they perceive
are continued, external, and independent (Fasko forthcoming).



With regard to continued existence, a mass of sensations exhibits many
series of sensible qualities that recur. For instance when you look at
a house while walking by, you are conscious of a series of visual
images and if you happen to retrace your steps, the same series
appears in reverse order. Shepherd argues that whenever we are
conscious of a series of sensible quality sensations that is repeated,
we comprehend that each repetition must have a cause that continues to
exist "ready to answer the irregular call of the senses"
(EPEU: [2020: 15-16]). Otherwise, each would have a cause
created explicitly for the purpose of being ready to mix with sensory
organs when needed; or if not, different recurrences would begin of
themselves. Consciousness of his reasoning enables us to have an idea
of existence continued unperceived but only consciousness of
interrupted sensations (EPEU [2020: 134]).



We say we perceive "external" objects. Shepherd offers to
clarify the difference between what is external and internal:
."Inward existence is the capacity for sensation in general;
outward existence is the exciting cause of some sensation in
particular" (EPEU [2020: 40]). The capacity for sensation in
general is the mind. The cause of a particular sensation results from
the mixing of the mind and an object that needs to be outside the mind
in order to mix with it. Accordingly, sensations are inward,
interrupted, and can be known by only one subject, whereas what is
outward has continued existence and can be perceived by more than one
human being, if other human beings are possible (EPEU [2020: 40]). So
one reason to believe that the causes of sensible quality sensations
exist outside the mind is that we infer it from the belief that they
continue to exist unperceived. Others are offered as well.



Shepherd takes a particular interest in explaining why, despite our
conviction that sensations exist if only if they are perceived, we
somehow assume that sensations exist outside the mind. For instance, a
colored, figured, extended object is commonly considered to exist in
its colored, figured, extended state when it is no longer perceived.
Yet color, figure and extension are mental affections (EPEU [2020:
39]). Shepherd denies that this can be understood or even believed
because of its manifest impossibility. The doxastic performance is
said to be due to our belief that the particular object that causes a
particular sensible quality must be outside the mind, on one hand, and
the paucity of our resources for recalling the object, on the other
hand. After we perceive, say, an apple, our only way to think of it or
distinguish it from other objects is under the form of its sensible
qualities. This is said to produce a natural association of thought
that links sensations and their causes so tightly that philosophical
analysis is required to pry them apart. She reports several
extravagant and mutually inconsistent theories philosophers have
proposed in the effort to separate sensations and objects outside the
mind; Reid, Malebranche, Leibniz, as well as Berkeley and Hume are
mentioned (EPEU [2020: 45-6]). She easily uncouples the
association by stressing the difference between inward and outward
existence based on her theory of the relation of cause and effect
(EPEU [2020: 71, 114]).



Shepherd advances three reasons that motivate belief that perceptual
objects are mind
 independent.[4]
 One is that we believe objects we perceive undergo change of sensible
qualities when we are not perceiving them. Another is, in brief, we
believe there are beings like ourselves who have the power of thought
and feeling, and we perceive that one external object can affect many
such beings; (EPEU [2020: 76-81]). She also constructs an
argument intended to show that we can form an abstract general idea of
existence, or the notion of "indefinite unknown existence"
which enables us to have thoughts of continued, external, and entirely
independent existence (EPEU [2020: 82-26]).


### 3.3 The phenomena of dreams and only possible basis of skepticism



The phenomena of dreams are thought to pose an objection to belief in
the existence of the external world because we may credit the illusory
images with continued, external, independent existence. This is reason
to doubt the existence of all perceptual objects unless we have better
evidence for their reality than we have for that of the seeming
objects of dreams. Shepherd dispatches the objection. She grants that
sensations that occur in dreams are like those that occur in waking
experience although she denies that dreams can cause the same
sensations in the same order as those caused by objects existing in
nature (EPEU [2020: 99-100]). She argues that when dreaming, a
person's ability to collect a large number of sensations is
limited. When awake, we can move our eyes and limbs and find the
supposed object does not fulfill its definition (e.g. EPEU [2020:
29-33]). She allows that assuming we are awake, it is difficult
to know whether an object that has fulfilled its presumed definition
so far will do so later on. Judgments on this question can be
supported by observations that make them more or less probable and
thus subject to an appropriate level of doubt (ERCE [2020:
99-114]). Still, she admits there is one (but only one) possible
basis for skepticism about the reality of perceptual objects:
experience cannot show that the causes of all a person's
sensations are not necessarily mixed with the causes of her dreams
(EPEU [2020: 118-19]).


## 4. Mind, body, and self


### 4.1 Minds and bodies



Mind is the capacity for sensation in general, that is, the capacity
for thought and feeling. We ourselves are individual minds (EPEU
[2020: 14, 24]). Many of Shepherd's predecessors hold that the
potentiality of causal capacities is ultimately grounded in substances
in which the capacities inhere. Shepherd rarely uses the term
"substance" (but see EPEU [2020: 388]; ERCE [2000: 162)
but she ascribes a substance-like property to minds. This is the
upshot of two arguments based on the idea that the mind is a dual
capacity, for both particular sensations, which continuously vanish
and are followed by others, and for sensation as such, which is
resumed after periods of dreamless sleep. The argument comes down to
this: there would be no reason for the existence of sensation unless
there were a continuous being that is specifically "indifferent
to sensations [and] capable of being excited when interfered with by
qualities fitted to produce it.--Such a being is the subject of
successive sensations,--such is the capacity for
sensation,--such is the mind" (EPEU [2020: 375-6;
also 56-7]). A mind endures--it is one subject of different
successive states each dependent for existence on it. But unlike a
traditional substance, its successive states are effects rather than
powers; it is a dispositional rather than categorical entity; and a
mind is external to each of its states and can exist with no states at
all. "Thus the pronoun *I* is ever abstract and stands
for a BEING exterior to, and independent of all the changes of which
it is conscious." (EPEU [2020: 57]). This seems to show Shepherd
has no use for traditional substances (see LoLordo (forthcoming); but
Boyle 2020: 101, note 19; 104) finds that minds inhere in natures in
the substance theoretical sense.).



The conclusion that a mind is the continually existing subject of
successive states proves its eternality. It seems the "mysterious
eternal power of feeling" is inherited by each individual member
of a species: "as a continuous existence it must be an eternal
power in nature and as immortal for the future as it must have been
without beginning in the past" (EPEU [2020: 377]). This is
motivated by an implicit appeal to CP: "there would be no
reason", i.e. cause, for sensations if there were no continuing
subject matter ready to be interfered with by other suitable objects
(EPEU [2020: 375-6]), partly quoted in the previous paragraph;
[2020: 56-7]). More generally, it is a principle of
Shepherd's metaphysics that capacities for being are eternal
(EPEU [2020: 389-390]). Matter and time are eternal capacities
(EPEU [2020: 127, 389-390]). The consequences of this principle for
the causal structure of the universe have not, to my knowledge, been
discussed in the literature. Shepherd uses the principle in stating
her argument for the existence of God (EPEU [2020: 389-392; also
190-191]). This argument, which includes a version of the teleological
argument used to show there must be an eternal entity with mental
powers, purports to show that God is the continuously existing subject
of all changes (Loscano (2019) offers an account). The details of the
dependence relation between the infinite subject of all changes and
the objects that begin and cease to exist in nature are of
considerable interest. LoLordo (forthcoming) brings out similarities
to Spinoza's metaphysics; Garrett (forthcoming) considers it in
connection with the question whether Shepherd is able to reconcile her
denial of idealism with the causality of God, but finds the texts
inconclusive.



Shepherd argues that minds are not material beings on the evidence
that bodies in general do not feel in circumstances in which
individual minds do, e.g. a rock does not feel pain when it breaks.
According to Shepherd: "the definition of matter is *the
capacity of exhibiting upon a sentient nature, the sense of solid*
EXTENSION in general", and "that of mind, *a capacity
fitted to be excited to any sensation in particular*" (EPEU
[2020: 242]). To be clear, solid extension is a sensation; its name is
given also to the unknown powers of external objects that partly cause
it (Shepherd (1832); EPEU [2020, 697]). Accordingly, matter is also
defined as the capacity for unperceived motion (EPEU [2020: 14-16]).
On Shepherd's theory, mind and matter do not have mutually
incompatible absolute essences, as Descartes maintains; their absolute
"real essences" are unknown (EPEU [2020: 242-244]).
Nor is mind-body causal interaction a problem. If a mind and organized
matter form a union, each capacity realizes the other; a human being
has powers to feel, think, move and resist motion just as other kinds
of objects are defined by a number of different powers (EPEU [2020:
310-311]). Within a human being, Shepherd explains, a conscious
sensation of forming a plan and deciding to carry it out is united
with all the powers that co-exist with it, so the bodily part of the
human being starts a motion which is guided by the conscious decision;
the cause of this motion must satisfy CSP, but the efficient cause of
an effect is always unknown on her theory (EPEU [2020:
403-405]). See LoLordo (forthcoming) for further comparison of
this theory and mind-body substance dualism.)


### 4.2 Selves



According to Shepherd, we are individual capacities for sensation in
general (EPEU [2020: 14, 42)] who use "I" to refer to a
capacity external to all the sensations of which we are conscious
(EPEU: 56-7). Although Boyle (2020: 105) is right that it seems
reasonable that "I" refers to oneself, Shepherd wants to
say a self is a much more complex entity, an enduring object
with physical and psychological powers that mixes with other
objects with the result that various feelings, thoughts, bodily
motions, and mechanical interactions with external objects are
registered in it. A self comprises particular sensations including
consciousness of its continued existence, that is the feeling of the
continued existence of its mind and its body. Consciousness of the
former is analyzed as, first, the sensation of the idea of the
continually existing (partial) cause of sensations and, second, 
consciousness of the power to remember previous sensations, i.e. the
feeling of the power to unite a present sensation with the idea of a
past sensation (mass of qualities) and the passage of time (EPEU
[2020: 98, 153-154, 133). Consciousness of the continued
existence of the body is the sense of the extension of the body and
its being sufficient to sustain the powers of life and consciousness,
"especially those which determine the union of memory with sense"
(EPEU [2020: 153-154). The upshot is that our belief that we can
remember our previous mental states gives us the sense of our identity
over time. Shepherd offers no account of personal identity as such,
but she concludes: "identity, therefore, has nothing to do with
sameness of particles", or physical constituents of the self. It
is not incorrect to say the sense of identity depends on the power of
memory, but more fundamentally, it depends on the eternality of an
individual human mind (compare LoLordo (forthcoming)).



What happens to an individual mind when its present body dies? The
individual mind is immortal, but it is uncertain whether it will
remain dormant, "lost in the eternal ocean of mind" or
"retain its individual consciousness of personality" (EPEU
[2020: 378]), In the latter case, it may mix with some matter to form
the cause of new sensations and sustain the power to unite ideas of
memory with its present sensations or it may mix with some other sort
of entity to produce sensations detached from memory; even now we use
knowledge when we have forgotten how we got it (see LoLordo
(forthcoming) for a more detailed discussion). Although Shepherd
mentions analogies that make it probable that memory and personality
will be restored, she finds philosophy can go no further than that
(EPEU [2020: 379-88]).