## 1. Overview



Experimental philosophy is a relatively new approach, usually
understood as beginning only in the early years of the 21st century.
At the heart of this new approach is the idea of pursuing
philosophical questions using methods more typically associated with
the social sciences.



Within the broad banner of experimental philosophy research, one finds
work using an enormous variety of methods and aims (see, e.g.,
Schwitzgebel & Rust 2014; Meskin et al. 2013; Bartels &
Urminsky 2011). Nonetheless, most research in experimental philosophy
makes use of a collection of closely connected methods that in some
way involve the study of intuitions. The remainder of this section
aims to characterize the different projects experimental philosophers
have pursued using these methods and their relevance for broader
questions in philosophy.



The practice of exploring intuitions has its origins in a more
traditional philosophical approach that long predates the birth of
experimental philosophy (see the entry on
 intuition).
 Research within this more traditional approach often relies on the
idea that we can make progress on one or another topic by looking at
intuitions about that topic. For example, within epistemology, it has
been suggested that we can make progress on questions about the nature
of knowledge by looking at intuitions about whether certain states
count as knowledge. Similarly, within moral philosophy, it has been
suggested that we can make progress on questions about moral
obligation by looking at intuitions about what actions certain agents
are obligated to perform. Similar approaches have been advocated in
numerous other areas of philosophy.



There is a complex literature within the analytic tradition about how
to understand this traditional method. Some argue that the study of
intuitions gives us insight into concepts (Jackson 1998), others argue
that the study of intuitions gives us a more direct sort of insight
into the actual properties or relations those concepts pick out (Sosa
2007), and still others argue that this whole way of conceiving of the
project is a mistaken one (e.g., Cappelen 2012).



It is commonplace to divide existing research in experimental
philosophy into distinct projects in accordance with their different
relationships to this prior tradition. Dividing things up in this way,
one arrives at three basic kinds of research in experimental
philosophy.



First, some experimental philosophy research has a purely
'negative' relationship to this more traditional use of
intuitions. Such research aims to provide evidence that the method
used in the more traditional work is in some way flawed or unreliable.
For example, it has been argued that intuitions differ across
demographic factors such as gender or ethnicity, or that they are
subject to order effects, or that they can be influenced by incidental
emotion (e.g., Weinberg et al. 2001; Buckwalter & Stich 2014; Swain et
al. 2008; Cameron et al. 2013). To the extent that intuitions show
these effects, it is argued, we should not be relying uncritically on
intuition as a method for addressing substantive philosophical
questions. This first project is called 'negative' in that
it is not intended to make progress on the original philosophical
question (e.g., about the nature of knowledge) but only to argue
against a specific method for addressing that question (appeal to
intuition).



This project has triggered a large and multi-faceted literature among
philosophers interested in its metaphilosophical implications (Brown
2013b; Cappelen 2012; Deutsch 2015; Weinberg 2007; Weinberg et al.
2010; Williamson 2007). This literature has explored the question as
to whether empirical facts about the patterns in people's
intuitions could give us reason to change our philosophical practices.
Much of this work is quite closely tied to prior philosophical work
about the role of intuition in philosophy more generally.



Second, some research in experimental philosophy aims to make further
progress on precisely the sorts of questions that motivated prior work
within analytic philosophy. Thus, this research looks at epistemic
intuitions as a way of making progress in epistemology, moral
intuitions as a way of making progress in moral philosophy, and so
forth. Experimental philosophers pursuing this second project have
offered various different accounts of the way in which facts about
intuitions could yield progress on these philosophical issues, but the
most common approach proceeds by advancing some specific hypothesis
about the underlying cognitive processes that generate intuitions in a
particular domain. The suggestion is then that this hypothesis can
help us assess which intuitions in this domain are worthy of our trust
and which should simply be dismissed or ignored (Gerken 2017; Leslie
2013; Greene 2008; Nagel 2010).



Work within this second project has inspired a certain amount of
metaphilosophical debate, but its main impact on the philosophical
literature has been not at the level of metaphilosophy but rather in
discussions of individual philosophical questions. Thus, philosophers
interested in epistemic contextualism discuss experiments on
people's intuitions about knowledge (DeRose 2011), philosophers
interested in incompatibilism discuss experiments on people's
intuitions about free will (Bjornsson & Pereboom 2014; Vargas
2013), and philosophers interested in interventionist accounts of
causation discuss experiments on people's intuitions about
causation (Woodward 2014). Work in this vein typically does not focus
primarily on more abstract theories about the role of intuitions in
philosophy. Instead, it draws more on theories about the particular
topic under study (theories of knowledge, free will, causation).



The third type of research being conducted in experimental philosophy
is not concerned either way with the kind of project pursued in more
traditional analytic philosophy; it is just doing something else
entirely. Specifically, in many cases, experimental philosophers are
not looking at people's thoughts and feelings about some topic
as a way of making progress on questions about that topic; they are
instead trying to make progress on questions that are *directly
about people's thoughts and feelings themselves*. For
example, much of the experimental philosophy research in moral
psychology is concerned with questions that truly are about moral
psychology itself.



Research in this third vein tends to be highly interdisciplinary.
Thus, work on any particular topic within this third vein tends to be
at least relatively continuous with work on that same topic in other
disciplines (psychology, neuroscience, linguistics, etc.), and the
impact of such work is often felt just as much in those other
disciplines as in philosophy specifically.



The distinction between these projects has proven helpful within
metaphilosophical work on the significance of experimental philosophy,
but it should be noted that the metaphilosophical distinction between
these three projects does not correspond in any straightforward way to
the distinctions between the different concrete research programs
experimental philosophers pursue (on free will intuitions, on moral
intuitions, on epistemic intuitions, etc.). Each of these concrete
research programs can be relevant to a number of different projects,
and indeed, it often happens that a single paper reports a result that
seems relevant to more than one of these projects. Thus, as we review
the actual experimental research coming out of experimental
philosophy, we will need to turn away from the metaphilosophical
distinction between projects and turn instead to distinctions between
concrete research topics.


## 2. Research in Experimental Philosophy



The best way to get a sense of what experimental philosophy is all
about is not just to consider it in the abstract but to look in detail
at a few ongoing research programs in the field. Accordingly, we
proceed in this section by reviewing existing research in four
specific areas: the negative program, free will, the impact of moral
judgment, and epistemology.



We focus on these four areas because they have received an especially
large amount of attention within the existing experimental philosophy
of literature. We should note, however, that experimental philosophers
have explored an enormous range of different questions, and work in
these four specific areas comprises only a relatively small percentage
of the experimental philosophy literature as a whole.


### 2.1 The Negative Program



In the *Theaetetus,* Socrates asks, "Herein lies the
difficulty which I can never solve to my satisfaction--What is
knowledge?" (146a). The subsequent philosophical discussion often
proceeds by setting out various hypotheses, e.g., that knowledge is
true belief, and considering possible counterexamples to the
hypothesis. So, for instance, Socrates argues that knowledge
isn't simply true belief because a skilled lawyer can persuade a
person to have a belief that is true, but that belief wouldn't
actually be knowledge [see the entry on the
 Theaetetus].
 Socrates typically expects, and receives, agreement from his
interlocutor. Nor does Socrates ask his interlocutor, "What is
*your* conception of knowledge" or "What counts as
knowledge for Athenians?" Rather, he seems to expect a global
answer about what knowledge is. In addition, he seems to expect that
knowledge has a single nature, as suggested by his telling Theaetetus,
"I want you... to give one single account of the many
branches of knowledge" (148d).



Work in the *negative program* of experimental philosophy uses
empirical work to challenge this traditional philosophical project.
Two somewhat different challenges have been developed.


#### 2.1.1 The argument from diversity



One challenge arises from the prospect of systematic diversity in how
different populations of people think about philosophical questions.
The possibility of such diversity had been raised before (e.g., Stich
1990), but experimental philosophers have sought to provide evidence
of such diversity. For instance, an early study reported differences
between East Asian students and Western students on famous cases from
epistemology (Weinberg et al. 2001). Another early study provided
evidence for cultural differences in judgments about reference. East
Asians were more likely than Westerners to have descriptivist
judgments about the reference of proper names (Machery et al. 2004).
Some studies have also found gender differences in intuitions about
philosophical cases (see, e.g., Buckwalter & Stich 2014; Friesdorf
et al. 2015). In addition, there are systematic individual differences
in philosophical intuition; for example, people who are more
extraverted are more inclined to compatibilism about responsibility
(Feltz & Cokely 2009).



This apparent diversity in intuitions about philosophical matters has
been used to challenge the use of intuitions in philosophy to tell us
about the nature of things like knowledge and reference. If intuitions
about knowledge turn out to exhibit diversity between populations,
then this looks to put pressure on a traditional philosophical
project. In rough form, the worry arises from the following
claims:


* D1. The philosophical
tradition uses intuitions regarding philosophically important
categories or kinds like *knowledge* in an effort to determine
the nature of those categories
* D2.  *Knowledge*
(like many other philosophical categories) has a single nature.
It's not the case that knowledge is one thing in Athens and
another thing in Sparta.
* D3.  Intuitions about
philosophical categories systematically vary between populations (by
culture, for instance)
* D4.  The diversity in
intuition cannot be dismissed by privileging the intuitions of one
population.



Each of these claims has been challenged. Some argue that philosophers
do not--or should not--rely on intuitions (thus rejecting
D1) (see
 section 3.1);
 others hold, contra D4, that certain populations (e.g., professional
philosophers) are specially positioned to have reliable intuitions
(see
 section 3.2).



Another way to defuse the challenge is to argue (contra D2) that we
needn't suppose that *knowledge* has a single nature, but
instead allow for a kind of pluralism. For instance,
"knowledge" might pick out different epistemic notions in
different communities. A pluralist might allow, or even celebrate,
this diversity. Even if other communities have different epistemic
values than we do, this need not undermine our valuing knowledge, as
it is construed in our community (e.g., Sosa 2009: 109; also Lycan
2006). For a pluralist, empirical demonstrations of diversity
needn't undermine traditional philosophical methods, but might
instead reveal important epistemic features that we have missed.



A more conservative response to the challenge, which leaves
traditional philosophy largely untouched, is to question whether there
really is diversity between populations in intuitions about
philosophical categories. One way to develop this response is to claim
that participants in different populations might simply interpret the
scenarios in different ways; in that case, we could explain their
different answers by saying that they are responding to different
questions (e.g., Sosa 2009). 



More importantly, a growing body of empirical evidence has called into
question the claim that there really are large differences in
philosophical intuitions across populations. Some of the original
findings of culture differences have not replicated (e.g., Nagel et
al. 2013; Kim & Yuan 2015); similarly, many of the original
findings of gender differences haven't replicated (e.g.,
Seyedsayamdost 2015; Adleberg et al. 2015). These findings provide
strong reason to believe that some of the effects suggested by early
experimental philosophy studies do not, in fact, exist at all.
Moreover, experimental philosophers have also uncovered robust
cross-cultural uniformity. For instance, one recent cross-cultural
study examined intuitions about Gettier cases across four very
different cultures (Brazil, India, Japan, and the USA), with
participants in all groups tending to deny knowledge to the
protagonist in Gettier cases (Machery et al. 2015). This suggests that
there might be a universal "core folk epistemology"
(Machery et al. 2015). In any case, these kinds of results suggest
that there is less diversity than had been suggested.


#### 2.1.2 The argument from sensitivity



The foregoing argument is based on diversity between populations. But
experimental philosophers in the negative program have also used
intra-individual diversity to undermine traditional philosophical
methods (Swain et al. 2008; Sinnott-Armstrong 2008; Weinberg
2016).
Experimental philosophers have found that people's judgments
about philosophical cases are sensitive to various kinds of contextual
factors that seem to be philosophically irrelevant. The same person
will give different responses depending on apparently irrelevant
factors of presentation. People's judgments about cases are
affected by the induction of irrelevant emotions (Cameron et al.
2013), the order in which cases are presented (Petrinovich and
O'Neill 1996; Swain et al. 2008; Wright 2010), and the way an
outcome is described (e.g., Petrinovich and O'Neill 1996;
Schwitzgebel & Cushman 2015).



Sensitivity to contextual factors has been used to challenge the
philosophical use of intuition in a way that is somewhat distinct from
the diversity argument. The challenge begins with the same assumption
about the role of intuitions in philosophy, but then draws on somewhat
different considerations:


* S1.  The philosophical
tradition uses intuitions regarding philosophically important
categories or kinds like *knowledge* in an effort to determine
the nature of those categories
* S2.  A person's
judgments about philosophical cases are sensitive to contextual
factors like the order of presentation.
* S3.  Sensitivity to
these factors is epistemically inappropriate
* S4.  This inappropriate
sensitivity cannot be dismissed by privileging the intuitions of one
population (e.g., philosophers)
* S5.  We can't
tell, from the armchair, which of our judgments are inappropriately
sensitive in this way.



This set of claims presents a challenge because it seems that even
philosophers are susceptible to these epistemically inapt influences,
and we can't tell which of our intuitions are to be trusted.
Thus, philosophers are on shaky epistemic ground when they rely on
their intuitions to try to glean philosophical truths.



Obviously, the argument from sensitivity is developed in different
ways depending on the category in question and the evidence of
sensitivity, but it's useful to see how the general claims
(S1-S5) might be questioned. (See
 section 3.1
 for the rejection of intuition in philosophy (S1) and
 section 3.2
 for a defense of privileged populations [contra S4]).



Although there are replicable effects on the influence of contextual
factors, *pace* S2 many of these effects seem too small to
threaten the practice of relying on intuitions (see, e.g.,
Demaree-Cotton 2016; May 2014). The effect might amount to the
difference between 2.2 and 2.5 on a 7 point scale. It's hard to
see how such a difference threatens the practice of relying on the
operative intuitions.



In some cases, contextual factors have more pronounced effects, and do
lead to changes in participants' verdict about a case. For
instance, judgments about certain moral dilemmas and judgments about
certain epistemic cases are changed depending on previously seen cases
(e.g., Petrinovich & O'Neill 1996; Swain et al. 2008).
However, it's possible that participants respond differently to
a case because the contextual differences actually provide an
epistemically appropriate basis for changing one's judgment. For
instance, in the order effect studies, seeing one case can provide
*evidence* about the appropriate response on another case
(Horne & Livengood 2016). On this view, we can grant that
participants change their judgment, but deny that they are doing so in
a way that is epistemically inappropriate.



Finally, even if people's judgments do change in epistemically
inappropriate ways, people might be able to recognize which judgments
are especially trustworthy. For instance, only some thought
experiments are susceptible to order effects, and it turns out that
for these thought experiments, people have lower confidence in their
responses (e.g., Wright 2010; Zamzow & Nichols 2009). This
suggests (contra D5) that there might be an internal
resource--confidence--that can be used to discern which
judgments are epistemically unstable.


### 2.2 Free Will and Moral Responsibility



Research in experimental philosophy has explored many aspects of lay
beliefs regarding free will. Experimental philosophers have designed
improved scales for measuring belief in free will (Nadelhoffer et al.
2014; Deery et al. 2015), they have investigated the role of the
desire to punish in attributing free will (Clark et al. 2014), and
they have examined the impact of the belief in free will on moral
behavior (Baumeister et al. 2009). But the most intensively studied
issue concerns intuitions about whether free will is compatible with
determinism.



Experimental philosophers have argued that the philosophical defense
of incompatibilism depends on intuitions (e.g., Nahmias et al., 2006).
The question about whether incompatibilism is true depends on a wide
variety of factors, but experimental philosophers have argued that one
factor that plausibly matters is the alleged intuitiveness of the
thought that determinism is incompatible with free will (Murray &
Nahmias 2014, but see Sommers 2010). This then generates a question
that invites an empirical inquiry: *is incompatibilism
intuitive?* (Nahmias et al. 2006).



One of the first experimental studies on free will found that people
seemed to have compatibilist intuitions. Participants were presented
with a scenario describing a deterministic universe, and then asked
whether a person in the scenario was free and morally responsible
(Nahmias et al. 2006). In one case, participants were asked to imagine
a future scenario in which there is a supercomputer that is capable of
predicting all future human behavior when provided with a complete
description of the universe along with the laws of nature. In this
scenario, a man robs a bank, and participants are asked whether the
man is morally responsible for his action. Somewhat surprisingly, most
participants gave compatibilist answers, saying that the person was
morally blameworthy. This basic finding held across a number of
scenarios.



In these early studies on intuitions about free will and moral
responsibility, the description of determinism focused on the fact
that in a deterministic universe, every event is in principle
predictable from the past and the laws. In addition, the scenarios
involved particular agents in our world doing bad things. Later
studies emphasized the *causal* nature of
determinism--that what happens at a given point is *completely
caused* by what happened previously--and stressed that what
happens in a deterministic universe is *inevitable* given the
past. Even with this description of determinism, participants still
tend to say that a specific concrete individual in such a universe who
commits a heinous crime is free and responsible (Nichols & Knobe
2007; Roskies & Nichols 2008). However, when asked a more abstract
question about whether it is possible in general for people in such a
deterministic universe to be free and responsible, participants tend
to say that morally responsibility is not possible in a deterministic
universe. This incompatibilist response was also found in a cross
cultural sample with participants from India, Hong Kong, Colombia, and
the United States (Sarkissian et al. 2010). In addition to the
abstract nature of the question, another important element seems to be
whether one is considering an alternate deterministic universe or
contemplating the possibility that our own universe is deterministic.
When led to consider our own universe as deterministic, participants
were more likely to say that people would still be morally responsible
(Roskies & Nichols 2008).



Thus, it seems like people give compatibilist responses under some
conditions and incompatibilist responses under others. One reaction to
this apparent inconsistency is to treat one set of responses as
defective. Some experimental philosophers maintain that it's the
incompatibilist responses that don't reflect people's true
judgments. The best developed version of this view maintains people
aren't affirming incompatibilist responses at all (Nahmias &
Murray 2011; Murray & Nahmias 2014). Instead, when people deny
free will and responsibility it's because they misunderstand the
description of determinism. In particular, people mistakenly interpret
the description of determinism to mean that our mental states lack
causal efficacy, that the production of our behavior
"bypasses" our mental states. That is, on this view,
people wrongly think that determinism means that a person will behave
as she does regardless of what she thinks, wants, or intends (Murray
& Nahmias 2014).



Of course, if people's mental states have no impact on their
behavior, that is an excellent reason to think that people
aren't morally responsible for their behaviors. So, if people
interpret determinism to mean *bypassing*, it is perfectly
rational for them to infer the lack of free will and responsibility
from bypassing. However, it seems to be a flat-out confusion to
interpret determinism as bypassing. Even if determinism is true, our
behavior might be caused (not bypassed) by our mental states. Thus, if
people give incompatibilist responses because they confuse determinism
with bypassing, then people's responses don't reflect a
real commitment to incompatibilism.



Surprisingly, people *do* make bypassing judgments when given a
description of causal determinism. For instance, when presented with a
description of a determinist universe, many participants agreed that
in that universe, "what a person wants has no effect on what
they end up doing" (Murray & Nahmias 2014). This suggests
that people go through the following confused process: determinism
means bypassing, and bypassing means no free will. If that's
right, then the incompatibilist response really is a confusion.
However, another explanation is that people think that determinism
means no free will, and it's the denial of free will that leads
to the bypassing judgments. The idea would be roughly that if we
don't have free will, then in some way our mental states
don't lead to our behavior in the way we had thought. Some
experimental philosophers have used statistical causal modeling to try
to tease these two possibilities apart, arguing that it's the
latter explanation that is the right one (Bjornsson 2014; Rose
& Nichols 2013). That is, people take determinism to entail that
there is no free will, and it is this judgment that there is no free
will that leads to the bypassing judgment.



Thus, there is some reason to think that incompatibilist responses do
reflect many people's intuitions. What about the compatibilist
responses? Some experimental philosophers maintain that it is these
judgments that are distorted. On one view, the distortion is caused by
emotional reactions (e.g., Nichols & Knobe 2007). However, a
meta-analysis indicates that there is very little evidence that
emotions play a critical role in generating compatibilist judgments
(Feltz & Cova 2014). A different argument for demoting
compatibilist judgments holds that many people who affirm free
will in deterministic scenarios lack any sensitivity to compatibilist
considerations, but instead will affirm free will even under
fatalistic conditions in which it is explicitly stipulated that
John's behavior is inevitable "regardless of the past
events in John's life and the laws of nature". (This view
is dubbed "free will no matter what"; Feltz & Millan
2015.) One line of argument based on these results is that if
people's attributions of free will are so insensitive, it can
hardly be said that people appreciate the consistency of free will and
determinism. However, subsequent studies found that in these
fatalistic scenarios, subjects who affirmed free will still tended to
think that the source of the action was in the agent, in harmony with
"source compatibilism" (Andow & Cova 2016).



Thus, the state of the evidence currently suggests that people do have
both incompatibilist and compatibilist intuitions. Future empirical
work might uncover more clearly what factors and processes draws
people in one direction or the other. There are also open questions
about whether the role of different psychological mechanisms in
intuitions about free will has implications for philosophical
questions for whether we are truly free and responsible.


### 2.3 Impact of Moral Judgment



It is common to distinguish between two kinds of judgments that people
make about morally significant situations. On one hand, people can
make straightforwardly *moral judgments* (e.g., judgments about
moral wrongness, about obligation, about blameworthiness). On the
other, they can make judgments that might be morally relevant but that
still appear to be in some important sense *non-moral
judgments* (about whether the agent acted intentionally, whether
she caused certain outcomes, whether she knew what she was doing). A
question now arises as to how to understand the relationship between
these two different kinds of judgments.



One possible view would be that the relationship is entirely
unidirectional. Thus, it might be thought that (a) people's
moral judgments depend on prior non-moral judgments, but (b)
people's non-moral judgments *do not* depend on prior
moral judgments. We can illustrate this view with the example of the
relationship between people's moral judgments and their
intentional action judgments. It seems clear that people's moral
judgments about whether an agent is deserving of blame might depend on
prior non-moral judgments about whether this agent acted
intentionally. However, one might think that things do not go in the
opposite direction. It is not as though your non-moral judgment that
the agent acted intentionally could depend on a prior moral judgment
that her action was wrong.



Although this view might seem intuitively compelling, a series of
studies in experimental philosophy have called it into question. These
studies suggest that people's moral judgments can impact their
judgments even about what might appear to be entirely non-moral
questions. Such results have been obtained for a wide variety of
different apparently non-moral judgments. 


* When an agent knows that she will bring about an outcome but is
not specifically trying to bring it about, people are more inclined to
say that she brought it about *intentionally* when it is
morally bad than when it is morally good (Knobe 2003).
* When an agent correctly believes that an outcome will arise but
is only correct in this belief as the result of a coincidence, people
are more inclined to say that she has *knowledge* when the
outcome is morally bad than when it is morally good (Beebe & Shea
2013; Buckwalter 2014).
* When an agent has a lot of positive emotion and a high opinion of
her life, people are less inclined to say that she is truly
*happy* when her life is morally bad than when it is morally
good (Phillips, Nyholm & Liao 2014).
* When a number of different factors are each individually
necessary for an outcome to arise, people are more inclined to regard
one of the factors as a *cause* when it is morally bad than
when it is morally good (Alicke 1992; Hitchcock & Knobe
2009).



Effects of moral judgment have also been observed on numerous other
judgments, including everything from action individuation (Ulatowski,
2012) to attributions of weakness of will (May & Holton 2012) to
the semantics of gradable adjectives (Egre & Cova
2015).



These findings might be philosophically relevant at two different
levels. On one hand, each individual effect might be relevant to
philosophical work that aims to understand the corresponding concept
or property. Thus, the findings about intentional action judgments
might be relevant to philosophical work about intentional action,
those about happiness judgments might be relevant to philosophical
work about happiness, and so forth. At the same time, the general
finding that moral judgment has this pervasive influence might be
relevant to philosophical work that focuses on the human mind and the
way people make sense of the world. For example, these findings could
help us to understand the nature of folk psychology or the
relationship between our ordinary folk theories and more systematic
scientific theories.



To make progress on these two issues, research has focused on trying
to understand why these effects arise. That is, researchers have aimed
to provide hypotheses about the precise cognitive processes that give
rise to the patterns observed in people's judgments. These
hypotheses then, in turn, have implications for philosophical
questions both about specific concepts and properties and about the
human mind.



Existing research has led to a proliferation of hypotheses, drawing on
theoretical frameworks from a variety of fields (see Cova 2016 for a
review of seventeen hypotheses about the intentional action effect).
Still, although there are numerous distinct specific hypotheses, it
seems that the basic approaches can be grouped into four broad
families.



First, it might be that the effect is *not truly driven by moral
judgment*. Existing studies show that people make different
judgments depending on whether the agent is doing something helpful or
harmful, but of course, there are many differences between helpful and
harmful actions other than their moral status. For example, a number
of researchers have argued that the effect is in fact driven by
people's beliefs about the mental states of the agents in the
vignettes (Sloman, Fernbach & Ewing 2012; Sripada & Konrath
2011). Agents will tend to have different sorts of mental states when
they are doing something helpful than when they are doing something
harmful, and it might be that this difference in mental states is
driving all of the observed effects.



Second, it might be that the effect is indeed driven by moral judgment
but that it is the result of an *error*. On this view, moral
considerations do not play any real role in the concepts at work here
(people's concepts of intentional action, of happiness, etc.).
Rather, people's judgments are being biased or distorted by some
further process which gets in the way of their ability to correctly
apply their own concepts. For example, some researchers have argued
that the effect is due to a process of motivated cognition (Alicke,
Rose & Bloom 2011). People believe the agent to be blameworthy and
want to justify that belief. This desire to justify blame then
distorts their judgments about what might seem to be purely factual
matters.



Third, it might be that the effect is driven by moral judgment and
doesn't involve an error but nonetheless *simply reflects a
fact about how people use words*, rather than a fact about their
application of the corresponding concepts. Researchers often make
inferences from facts about how people use certain words
('intentionally,' 'happy,'
'knows') about how people apply the corresponding concepts
(the concept of intentional action, of happiness, of knowledge).
However, it is also possible for factors to influence the use of our
words without influencing the use of these concepts, and some
researchers have suggested that this is the process at work in the
present effects. For example, it has been suggested that these effects
arise as a result of conversational pragmatics, with people trying to
avoid the pragmatic implicatures that would be generated by making
certain claims that are in fact literally true (Adams & Steadman
2004). Alternatively, it has been suggested that the relevant words
(e.g., 'intentionally') are actually associated with more
than one different concept and that the impact of morality arises not
because morality plays a role in any of these concepts but rather
because it plays a role in the way people resolve the ambiguity of the
word itself (Nichols & Ulatowski 2007). On these sorts of views,
people are not necessarily making a mistake when their use of language
is impacted by moral judgment, but all the same, moral judgment is not
playing a role in their more basic capacities to make sense of the
world.



Fourth, it might be that *moral judgment actually plays a role in
people's basic capacities to apply the relevant concepts*.
For example, it has been argued that the concept of happiness is
itself a value-laden concept (Phillips et al. 2014). Similarly, it has
been suggested the concepts of intentional action and causation make
use of a form of counterfactual thinking in which moral judgments play
a key role (Icard, Kominsky & Knobe 2017; Phillips, Luguri &
Knobe 2015). On this last view, the effects observed in these
experiments point to a genuine role for moral judgment in the most
basic capacities underlying people's application of the relevant
concepts.



Debates between these rival views remain ongoing. Within the more
recent literature, discussion of these questions has become
increasingly interdisciplinary, with many of the key contributions
turning to methods from cognitive neuroscience, developmental
psychology, or computational cognitive science.


### 2.4 Epistemology



Within experimental work in epistemology, the primary focus of
research has been on the patterns of people's ordinary
attributions of *knowledge*. As we've seen
 (section 2.1),
 evidence on epistemic intuitions plays a prominent role in the
negative program. But work in experimental epistemology has not been
dominated by any one single issue or question. Rather, it has been
divided among a number of different strands of research, which have
each been pursued separately.



One important topic has been the role of *stakes* in
people's knowledge attributions. Suppose that Keith considers
some available evidence and then concludes (correctly) that the bank
will be open on Saturday. Now consider two cases. In the
*low-stakes* case, it is not especially important whether the
bank actually is open. By contrast, in the *high-stakes* case,
Keith's whole financial future depends on whether the bank is
open or not. The key question now is whether this difference in stakes
has any impact on whether it is correct to say: "Keith knows
that the bank will be open". 



Within the non-experimental literature, philosophers have appealed to
a wide variety of arguments to help resolve this question. Although
many of these arguments do not directly involve people's
intuitions about cases (Brown 2013a; see also Fantl & McGrath
2009; Hawthorne 2004), some specifically rely on the empirical claim
that people would be more willing to attribute knowledge when the
stakes are low than when the stakes are high (DeRose 1992). Among
philosophers who accept this empirical claim, there has been
considerable debate about precisely how to explain the purported
impact of stakes (DeRose 1992; Hawthorne 2004; Rysiew 2001; Stanley
2005). 



Surprisingly, a number of early findings from the experimental
epistemology literature suggested that people's ordinary
knowledge attributions actually *don't* depend on stakes.
For example, people seem to say that Keith knows the bank will be open
on Saturday not only in the low-stakes case but also in the
high-stakes case (Buckwalter 2010; Feltz & Zarpentine 2010; May et
al. 2010). This experimental finding threatens to undermine the entire
debate within the non-experimental epistemology literature. After all,
if there is no effect of stakes, then there is no question as to how
to understand this effect.



Subsequent experimental work in this area has therefore focused on the
question as to whether the stakes effect even exists at all. Some have
criticized the early experiments that did not find an effect (DeRose
2011). Others have shown that although the effect does not emerge in
the experimental paradigms used by those early experiments, it does
emerge in other paradigms (Pinillos 2012; Sripada & Stanley 2012;
but see Buckwalter & Schaffer 2015, for a critique). Regardless of
how these debates are resolved, recent experimental work seems to have
established, at a very minimum, that the pattern of people's
epistemic intuitions is not quite the way it was assumed to be within
the previous non-experimental literature.



A second question concerns the relationship between knowledge and
belief. Clearly, a mental state can only count as knowledge if it
satisfies certain conditions that go beyond anything that would be
required for the state to count as belief. Thus, there can be cases in
which a person believes that *p* but does not know that
*p*. A question arises, however, as to whether the converse
also holds. That is, a question arises as to whether a mental state
must satisfy certain conditions to count as a belief that go beyond
what would be required for it to count as knowledge. Can there be
cases in which a person knows that *p* but does not believe
that *p*?



Strikingly, a series of studies suggest that people do attribute
knowledge in certain cases in which they would not be willing to
attribute belief (Myers-Schulz & Schwitzgebel 2013; see also
Murray et al. 2013; Rose & Schaffer 2013; Buckwalter et al. 2015;
Shields 2016). In one study, participants were given a vignette about
a student taking a history test who faces the question: "What
year did Queen Elizabeth die?" She has reviewed this date many
times, but at that one moment, she is flustered by the pressure and
can't recall the answer. She therefore decides just to guess,
and she writes down '1603.' In fact, this is the correct
answer. When given this vignette, experimental participants tended to
say that (a) the student *knows* that Queen Elizabeth died in
1603 but to deny that (b) she *believes* that Queen Elizabeth
died in 1603 (Myers-Schulz & Schwitzgebel 2013, drawing on a
vignette from Radford). Similar effects have been obtained for
numerous other cases (Murray et al. 2013; Rose & Schaffer 2013;
Buckwalter et al. 2015; Shields 2016).



Research in this area aims to understand why this effect arises and
what implications it has for epistemology. One view is that
people's concept of belief truly does involve certain conditions
that are not required by their concept of knowledge (Myers-Schulz
& Schwitzgebel 2013). An alternative view is that there is more
than one sense of 'belief,' such that knowledge requires
the mental state picked out by one of the senses but not the other.
Within work that adopts this latter approach, there have been a number
of more specific suggestions about how to spell out the difference
between the two senses and what relation each has to the ordinary
concept of knowledge (Rose & Schaffer 2013; Buckwalter et al.
2015).



Experimental epistemology has also explored numerous other issues. A
series of studies indicate that people actually do attribute knowledge
in 'fake barn' cases (Colaco et al. 2014; Turri
2017). Others show that judgments about whether a person's
mental state counts as knowledge depend on whether that person's
evidence comes from facts about an object itself or from statistical
base rates (Friedman & Turri 2015). Still others have explored
issues at the intersection of formal semantics and epistemology,
exploring the impact of specific linguistic factors on knowledge
attributions (Schaffer & Szabo 2014).


### 2.5 Other Topics



We have been focusing in on four specific areas in which there have
been especially prominent contributions from experimental philosophy,
but we should emphasize that it is not as though the majority of
experimental philosophy research falls into one or another of these
areas. On the contrary, research in experimental philosophy is highly
diverse, and it has actually been getting steadily more heterogeneous
in recent years.



First, experimental philosophers have been pursuing an ever more
diverse array of topics. On one hand, there has been a surge of
experimental research using more formal, mathematical tools, including
work on causation using Bayes nets (e.g., Livengood & Rose 2016).
and work in formal semantics on everything from gradable adjectives to
conditionals to epistemic modals (Liao & Meskin 2017; Cariani
& Rips 2017; Khoo 2015). On the other, there has been a
proliferation of work addressing core topics in the humanities,
including art, religion and even questions at the intersection of
experimental philosophy and the history of philosophy (De Cruz &
De Smedt 2016; Liao et al. 2014; Nichols 2015).



Secondly one finds an ever-growing diversity of experimental methods.
There are still plenty of studies that proceed by giving participants
vignettes and asking for their intuitions, but in contemporary
experimental philosophy, one also finds studies using corpora (Reuter
2011), reaction times (Philips & Cushman 2017), neuroimaging
(Greene et al. 2001), even
studies that look at whether ethics professors actually behave
ethically (Schwitzgebel & Rust 2014).



Finally, and perhaps most noticeably, there is an increasingly close
connection between research in experimental philosophy and research in
psychology. For example, the experimental research program on
intuitions about trolley problems has been dominated by contributions
from psychology (e.g., Cushman et al. 2006; Wiegmann et al. 2012), but
there have also been important contributions from philosophers (e.g.,
Mikhail 2011; Kahane & Shackel 2008). Conversely, there have been
numerous recent papers in psychology that aim to contribute to
research programs that originated in experimental philosophy (Samland
& Waldmann 2016; Feldman & Chandrashekar forthcoming; Starmans
& Friedman 2012). 


## 3. Challenges to Experimental Philosophy



As is the case with any healthy research area, there is lots of
dispute about issues within experimental philosophy. There are
disagreements about particular studies, the implications of different
kinds of results, and so on. But there are also broad challenges to
the very idea that experimental philosophy research could prove
helpful in addressing the philosophical questions. We focus here on
three of the most prominent of these challenges.


### 3.1 Disputing the Role of Intuitions in Philosophy



As we've seen, much work in experimental philosophy presupposes
that intuitions play an important role in philosophical inquiry. Work
in the negative program characteristically starts with the assumption
that intuitions play a central role in the philosophical tradition.
Outside of the negative program, experimental philosophers want to
understand what people's intuitions are about philosophical
matters and why they have these intuitions. Several philosophers,
however, challenge the role of intuitions in philosophy in ways that
also pose a challenge to the philosophical significance of much
experimental philosophy.


#### 3.1.1 Philosophers don't rely on intuitions



One way to reject the role of intuitions is simply to deny that
philosophers use intuitions as justification for their views
(Williamson 2007; Cappelen 2012; Deutsch 2009, 2010, 2015). According
to such "intuition deniers", the experimental
investigation of intuitions is thoroughly irrelevant to philosophy
(e.g., Cappelen 2012: 1; for discussion, Nado 2016). Obviously if this is right, then
the negative program is arguing against a thoroughly mistaken
conception of philosophy.



Although work in metaphilosophy often assumes that philosophers use
intuitions as evidence, this is exactly what is challenged by
intuition deniers. It is granted on all sides that philosophers
sometimes mention intuitions, but according to the intuition deniers,
intuitions are not integral to the philosophical work. In particular,
intuition deniers maintain that a careful inspection of philosophical
practice reveals that philosophers don't rely on intuitions to
justify philosophical views; rather, philosophers rely on
*arguments* (see, e.g., Cappelen 2012: 170; Deutsch 2009:
451).



There have been several responses to the intuition deniers, but
perhaps the most prominent response to is that the arguments of
intuition deniers depend on an implausibly strong conception of the
notion of *intuition* (e.g., Chalmers 2014; Devitt 2015;
Weinberg 2014). Once we focus on a less demanding notion of intuition,
it's plausible that philosophers often rely on intuitions as
evidence for philosophical theses (Devitt 2015). Indeed, some have
argued that for classic examples like Gettier cases, it's hard
to see how the argument works if it doesn't rely on intuitions
(see, e.g., Brown 2017; Sytsma & Livengood 2015: 92-93)
Experimental philosophers have also argued against intuition deniers
on experimental grounds, noting that a recent study found that over
50% of philosophers agree with the statement "intuitions are
useful for justifying philosophical claims" (Kuntz & Kuntz
2011; see Sytsma & Livengood 2015: 91).


#### 3.1.2 Philosophers shouldn't rely on intuitions



A rather different way to challenge the study of intuitions in
experimental philosophy is to deny that the study of intuitions is an
apt subject matter for philosophical inquiry. On this view, we can
grant that it's a fact that philosophers rely on intuitions, but
it's a lamentable fact. The use of intuitions in philosophy is
misguided for reasons that have nothing in particular to do with
experimental philosophy--the appeal to intuitions is a relic,
which should be rejected because it doesn't actually answer the
philosophical questions. This conclusion threatens positive
applications of experimental philosophy (see, e.g.,
 sections 2.2-2.4),
 but is of course, perfectly consistent with the conclusion urged by
the negative program in experimental philosophy
 (section 2.1).



One influential argument against the use of intuitions builds on the
rejection of descriptivist theories of reference, according to which
concepts refer to kinds via a set of associated descriptions. In place
of descriptivism, some maintain that concepts refer in virtue of the
function of the concept (e.g., Millikan 2000). Other views maintain
that concepts refer in virtue of a causal chain connecting the concept
to the kind (Putnam 1973). On these anti-descriptivist views, people
can have wildly mistaken intuitions regarding the application of their
concepts. As a result, probing lay intuitions might be an ineffective
way to investigate the kinds of things to which our concepts refer
(e.g., Fischer 2015; Kornblith 2002).



Anti-descriptivism itself doesn't entail that appeal to
intuitions is philosophically irrelevant. Indeed, some of the most
influential arguments against descriptivist theories of reference seem
to depend on intuitions (Devitt 2015). However, some argue that rather
than relying on intuitions about kinds, we should investigate the
kinds themselves. So, if the concept *knowledge* picks out a
natural kind, we can consult the distribution and characteristics of
knowledge as it is instantiated in the world. Using intuitions to
understand knowledge would be like using intuitions to
understand gold. The way we come to understand the nature of
gold is to examine samples of gold rather than people's
intuitions about gold. Similarly, the way to understand
knowledge is to examine samples of knowledge as it presents
in animals, rather than people's intuitions about knowledge
(Kornblith 2002). To examine knowledge by intuitions is at best
inefficient, and at worst a complete distraction from the task of
understanding what knowledge is. This objection is primarily directed
at traditional forms of conceptual analysis, but insofar as
experimental philosophy focuses on intuitions, it is in the same leaky
boat (Kornblith 2013: 197).



The claim that philosophers shouldn't rely on intuitions
constitutes a broad attack on conceptual analysis, in both its
traditional and experimental guises. Not surprisingly, there have been
several defenses of the importance of intuitions for doing philosophy.
For instance, some philosophers argue that in order even to pick out
the kind of interest, we need to rely on our intuitive sense of what
belongs in the category (e.g., Goldman 2015). To determine the
characteristics of knowledge, we need to have a way of picking out
which items are genuine members of the kind, and for this we must rely
on our intuitive understanding of knowledge. In addition, if we reject
outright the appeal to what intuitively belongs to a category,
it's hard to make sense of the intelligibility of eliminativism
(e.g., Bermudez 2006: 305), since eliminativists typically
argue that there is a mismatch between intuitive notions of, e.g.,
free will, and the kinds of things in the world. To give up on the
significance of characterizing our intuitive commitments is to
preemptively exclude eliminativist views, which have long been
regarded as of central philosophical interest.


### 3.2 Defending Privileged Intuitions Rather Than Those of Ordinary Experimental Participants



A second objection would be that even if intuitions do matter, we
should not be concerned with just any old kind of intuition. Rather,
our concern should be with a distinctive class of intuitions.
For example, research in philosophy has traditionally been conducted
by trained philosophers who spent years thinking about difficult
problems. There is good reason to suspect that the intuitions
generated by this type of process will have a special sort of
epistemic status, and perhaps these sorts of intuitions can play a
legitimate role in philosophy. By contrast, the intuitions explored
within experimental philosophy research tend to be those of ordinary
folks, with no prior background in philosophy, and one might think
that intuitions of this latter type have no real philosophical
significance.



One way of spelling out this concern is in terms of what has come to
be known as the *expertise objection*. The key contention here
is that trained philosophers have a distinctive type of expertise.
Thus, if we want to understand the process at the core of traditional
philosophical practice, we need to study people who have this type of
expertise. It is no good just looking at the judgments of people who
have never taken a single philosophy course. A number of philosophers
have developed objections along more or less these lines though with
important differences (Williamson 2007; Ludwig 2007).



This is an important objection, and to address it, experimental
philosophers launched a major effort to study the intuitions of
trained philosophers. The results show that trained philosophers still
show order effects (Schwitzgebel & Cushman 2012), actor/observer
effects (Tobia et al. 2013), and effects of temperament (Schulz,
Cokely, & Feltz 2011). Thus, existing work provides at least some
evidence against the claim that trained philosophers have a
distinctive expertise that allows them to escape the sorts of biases
that plague the judgments of ordinary folks.



Of course, there are numerous ways of defending the objection against
this type of response. It could be argued that although philosophers
do not have an ability to avoid biases of the type studied within
experimental philosophy, their judgments do differ from those of
ordinary folks in some other important respect. Similarly, it could be
argued that what gives certain intuitions their privileged epistemic
state is not the fact that they come from a particular type of person
(trained philosophers) but rather the fact that they are the product
of a particular way of approaching the question (sustained reflection)
(see, e.g., Kauppinen 2007).


### 3.3 But is it Philosophy?



Finally, it might be objected that experimental philosophy simply
isn't philosophy at all. On this view, there are certain
properties that differentiate work in philosophy from work in other
disciplines. Research in experimental philosophy lacks these
properties and is therefore best understood as falling outside the
philosophical tradition entirely. Note that this last objection is not
concerned with the question as to whether experimental philosophy has
any value but rather with the question as to whether it should be
considered part of a particular discipline. As one recent paper puts
it, 



> 
> 
> ... what is at issue is not whether there is room for such
> empirical study, but whether there is room for it now as a branch of
> *philosophy*. (Sorell forthcoming: 6)
> 
> 
> 



In actual practice, debate over this objection has tended to focus on
questions in the history of philosophy. Clearly, numerous philosophers
from Aristotle through Nietzsche were deeply concerned with empirical
questions about human nature, so it might seem that the default view,
at least in the absence of any counterarguments, should be that work
on these issues can indeed count as philosophy. The key question,
then, is whether there are any legitimate counterarguments.



One possible argument would be that although the people we now regard
as philosophers did work on these issues, this aspect of their work
should not be regarded as falling within the discipline of philosophy.
Anthony Appiah questions this gambit:



> 
> 
> You would have a difficult time explaining to most of the canonical
> philosophers that *this* part of the work was *echt*
> philosophy and *that* part of their work was not. Trying to
> separate out the "metaphysical" from the
> "psychological" elements in this corpus is like trying to
> peel a raspberry. (Appiah 2008: 13)
> 
> 
> 



According to this response, there is a well-established practice
within the history of philosophy of exploring empirical and
psychological questions, and it is actually the idea of carefully
separating the psychological from the philosophical that should be
regarded as a departure from philosophical tradition.



More recent work on these issues has been concerned especially with
the early modern period. It has been noted that some of the most
prominent philosophers in this period actually conducted experimental
studies (Sytsma & Livengood 2015), and some explicitly referred to
themselves as 'experimental philosophers' (Anstey &
Vanzo 2016). Though contemporary experimental philosophy obviously
differs in certain respects from these historical antecedents, one
might argue that the work of contemporary experimental philosophers is
best understood as a continuation of this broad historical
tradition.



On the other side, it has been argued that this historical continuity
picture fails to take account of a change in the use of the word
'philosophy' (Sorell forthcoming). In the Renaissance,
physics was referred to as 'philosophy,' but we would not
say that all research in contemporary physics belongs in the
discipline of philosophy. Similarly, even if work on the psychology of
moral judgment was historically classified as philosophy, one might
think that it should not be regarded today as falling into the
discipline of philosophy but rather into a distinct discipline.



Certainly, partisans on both sides of this debate should agree that
the boundaries of a discipline can change over time, but this point
cuts both ways. Just as the boundaries of a discipline may have
changed in the past, they can change in the future. It will therefore
be interesting to see how the boundaries of the discipline of
philosophy evolve over the course of the next few decades and how this
evolution impacts the status of experimental philosophy.