## 1. Varieties of Moral Skepticism




Moral skeptics differ in many ways (cf. Machuca 2017), but they share a common core that
makes them all moral skeptics. What makes moral skepticism
*moral* is that it concerns morality rather than other
topics. Moral skeptics might go on to be skeptics about the external
world or about other minds or about induction or about all beliefs or
about all norms or normative beliefs, but these other skepticisms are
not entailed by moral skepticism alone.




What makes moral skeptics *skeptics* is that they raise doubts
about common beliefs. Moral skeptics then differ in the kinds of
common beliefs that they doubt. They might, for example, doubt
categorical or absolute moral beliefs without doubting weaker kinds of
moral beliefs. Moral skeptics also differ in the kinds of doubts that
they raise. Since general skepticism is an epistemological view about
the limits of knowledge or justified belief, the most central version
of moral skepticism is the one that raises doubts about moral
knowledge or justified moral belief.




There are two main traditions in epistemological skepticism. One
tradition makes the claim that nobody ever knows or can know
anything. This claim is sometimes named *Cartesian* skepticism
(although Descartes argued against it) or *Academic* skepticism
(despite other interpretations of skeptics in the ancient
Academy). For lack of a better description, we can call
it *dogmatic* skepticism, because such skeptics dogmatically
assert a universal claim. In contrast, no such claim is made
by *Pyrrhonian* skeptics. They also don't deny any claim like
this. They have so much doubt that they refrain from taking any
position one way or the other on whether anyone does or does not or
can or cannot know anything.




Moral skepticism comes in two corresponding varieties. *Pyrrhonian
skeptics about moral knowledge* refuse to admit that some people
sometimes know that some substantive moral belief is true. They doubt
that moral knowledge is possible. Still, they do not go on to make the
opposite claim that moral knowledge is impossible. They doubt that,
too. Their doubts are so extreme that they do not make any claim one
way or the other about the actuality or possibility of moral
knowledge. Parallel views can be adopted regarding justified moral
belief. *Pyrrhonian skeptics about justified moral belief*
suspend or withhold belief about the actuality or possibility of any
justified moral belief.




In contrast, dogmatic moral skeptics make definite claims
about the epistemic status of moral beliefs:



*Dogmatic skepticism about moral knowledge* is the claim that nobody
ever knows that any substantive moral belief is true (cf. Butchvarov
1989, 2).





Some moral skeptics add this related claim:



*Dogmatic skepticism about justified moral belief* is the claim that
nobody is ever justified in holding any substantive moral belief.





(The relevant way of being justified is specified in
Sinnott-Armstrong 2006, chap. 4.) These two claims and Pyrrhonian moral
skepticism all fall under the general heading of *epistemological
moral skepticism*.




The relation between these two claims depends on the nature of
knowledge. If knowledge implies justified belief, as is traditionally
supposed, then skepticism about justified moral belief implies
skepticism about moral knowledge. However, even if knowledge does
require justified belief, it does not require *only* justified
belief, so skepticism about moral knowledge does not imply skepticism
about justified moral belief.




One reason is that knowledge implies truth, but justified belief does
not. Thus, if moral beliefs cannot be true, they can never be known to
be true, but they still might be justified in some way that is
independent of truth. As a result, skepticism about moral knowledge is
implied, but skepticism about justified moral belief is not implied,
by yet another form of moral skepticism:



*Skepticism about moral truth* is the claim that no
substantive moral belief is true.
 




This claim is usually based on one of three more specific claims:




*Skepticism about moral truth-aptness* is the claim that no
substantive moral belief is the kind of thing that could be either true or false.



*Skepticism about moral truth-value* is the claim that no
substantive moral belief is either true or false (although some moral
beliefs are the kind of thing that could be true or false).



*Skepticism with moral falsehood* is the claim that every
substantive moral belief is false.





These last three kinds of moral skepticism are not epistemological,
for they are not directly about knowledge or justification. Instead,
they are about truth, so they are usually based on views of moral
language or metaphysics.




Some philosophers of language argue that sentences like
"Cheating is morally wrong" are neither true nor false,
because they resemble pure expressions of emotion (such as "Boo
Knicks") or prescriptions for action (such as "Go
Celtics"). Such expressions and prescriptions are kinds of thing
that cannot be either true or false. Thus, if these analogies hold in
all relevant respects, then substantive moral beliefs are also not the
right kind of thing to be either true or false. They are not apt for
evaluation in terms of truth. For this reason, such linguistic
theories are often taken to imply skepticism about moral
truth-aptness. Views of this general sort are defended by Ayer (1952),
Stevenson (1944), Hare (1981), Gibbard (1990; cf. 2003), and Blackburn
(1993), although recent versions often allow some minimal kind of
moral truth while denying that moral beliefs can be true or false in
the same robust way as factual beliefs.




Such views are often described as *non-cognitivism*. That label
is misleading, because etymology suggests that cognitivism is about
cognition, which is knowledge. Since knowledge implies truth,
skepticism about moral truth-aptness has implications for moral
knowledge, but it is directly about truth-aptness and not about moral
knowledge.




Whatever you call it, skepticism about moral truth-aptness runs into
several problems. If moral assertions have no truth-value, then it is
hard to see how they can fit into truth-functional contexts, such as
negation, disjunction, and conditionals (Sinnott-Armstrong 2000). Such contexts are also
unassertive, so they do not express the same emotions or prescriptions
as when moral claims are asserted. Indeed, no particular emotion or
prescription seems to be expressed when someone says, "Eating
meat is not morally wrong" (cf. Schroeder 2010). Expressivists
and prescriptivists respond to such objections, but their responses
remain controversial (cf. Sinnott-Armstrong 2006, chap. 2).




Many moral theorists conclude that moral assertions express not only
emotions or prescriptions but also *beliefs*. In particular,
they express beliefs that certain acts, institutions, or people have
certain moral properties (such as moral rightness or wrongness) or
beliefs in moral facts (such as the fact that a certain act is morally
right or wrong). This non-skeptical linguistic analysis still does not
show that such moral claims can be true, since assertions can express
beliefs that are false or neither true nor false. Indeed, all
substantive moral assertions and beliefs are false (or neither true
nor false) if they claim (or semantically presuppose) moral facts or
properties, and if this metaphysical thesis holds:



*Skepticism about moral reality* is the claim that no moral
facts or properties exist.
 




Skepticism about moral reality is, thus, a reason for skepticism with
moral falsehood, as developed by Mackie (1977), or skepticism about
moral truth-value, as developed by Joyce (2001). Opponents of
such *error theories* often object that some moral beliefs must
be true because some moral beliefs deny the truth of other moral
beliefs. However, error theorists can allow a negative moral belief
(such as that eating meat is
*not* morally wrong) to be true, but only if it merely denies
the truth of the corresponding positive moral belief (that eating meat
*is* morally wrong). If such denials of moral beliefs are not
substantive moral beliefs (as denials of astrological beliefs are not
astrology), then error theorists can maintain that all
substantive moral beliefs are false or neither true nor false.




Error theorists and skeptics about moral truth-aptness disagree about
the content of moral assertions, but they still agree that no substantive moral
claim or belief is true, so they are both skeptics about moral
truth. None of these skeptical theses is implied by either skepticism
about moral knowledge or skepticism about justified moral
belief. Some moral claims might be true, even if we cannot know or
have justified beliefs about which ones are true. However, a converse
implication seems to hold: If knowledge implies truth, and if moral
claims are never true, then there is no knowledge of what is moral or
immoral (assuming that skeptics deny the same kind of truth that
knowledge requires). Nonetheless, since the implication holds in only
one direction, skepticism about moral truth is still distinct from
all kinds of epistemological moral skepticism.




Yet another non-epistemological form of moral skepticism answers the
question "Why be moral?" This question is used to raise
many different issues. Almost everyone admits that there
is *sometimes* some kind of reason to be moral. However, many
philosophers deny various universal claims, including the claims that
there is *always* some reason to be moral, that there is always
a distinctively
*moral* (as opposed to self-interested) reason to be moral,
and/or that there is always *enough* reason to make it
irrational not to be moral or at least not irrational to be moral.
These distinct denials can be seen as separate forms of *practical
moral skepticism*, which are discussed in more detail in the
following supplementary document:



Supplement on Practical Moral Skepticism





Practical moral skepticism resembles epistemological moral skepticism
in that both kinds of skepticism deny a role to reasons in
morality. However, epistemological moral skepticism is about reasons
for *belief*, whereas practical moral skepticism is about
reasons for *action*. Moreover, practical moral skeptics
usually deny that there is *always* enough reason for moral
action, whereas epistemological moral skeptics usually deny that
there is *ever* an adequate reason for moral
belief. Consequently, practical moral skepticism does not imply
epistemological moral skepticism. Some moral theorists do assume that
a reason to believe that an act is immoral cannot be adequate unless
it also provides a reason not to do that act. However, even if the
two kinds of reasons are related in this way, they are still
distinct, so practical moral skepticism must not be confused with
epistemological moral skepticism.




Overall, then, we need to distinguish the following kinds of
epistemological moral skepticism:




*Dogmatic skepticism about moral knowledge* = nobody ever knows that
any substantive moral belief is true.



*Dogmatic skepticism about justified moral belief* = nobody is ever
justified in holding any substantive moral belief.



*Pyrrhonian skepticism about moral knowledge* withholds assent from
both dogmatic skepticism about moral knowledge and its denial.



*Pyrrhonian skepticism about justified moral belief* withholds assent from
both dogmatic skepticism about justified moral belief and its denial.





We also need to distinguish these epistemological moral skepticisms
from several non-epistemological kinds of moral skepticism:




*Skepticism* *about moral truth* = no substantive
moral belief is true.



*Skepticism* *about moral truth-aptness* = no
substantive moral belief is the kind of thing that could be either true or false.



*Skepticism about moral truth-value* = no substantive moral
belief is either true or false (although some moral beliefs are the
kind of thing that could be true or false).



*Skepticism with moral falsehood* = every substantive moral belief is false.



*Skepticism about moral reality* = no moral properties or facts exist.



*Practical moral skepticism* = there is not always any or
enough or distinctively moral reason to be moral.




 These kinds of moral skepticism can be diagrammed as follows:



![diagram](graph.jpg)
Figure 1.




 Skepticism about justified moral belief will be the primary topic for
the rest of this entry, and I will refer to it henceforth simply as
moral skepticism.


## 2. A Presumption Against Moral Skepticism?




Opponents often accuse moral skepticism of leading to immorality.
However, skeptics about justified moral belief can act well and be
nice people. They need not be any less motivated to be moral, nor
need they have (or believe in) any less reason to be moral than
non-skeptics have (or believe in). Moral skeptics can hold
substantive moral beliefs just as strongly as non-skeptics. Their
substantive moral beliefs can be common and plausible ones. Moral
skeptics can even believe that their moral beliefs are true by virtue
of corresponding to an independent moral reality. All that moral
skeptics need to deny or doubt in order to be moral skeptics is that their (or anyone's) moral beliefs are
justified. This meta-ethical position about the epistemic status of
moral beliefs need not trickle down and infect anyone's
substantive moral beliefs or actions.



 Critics still argue that moral skepticism conflicts with
common sense. Most people think that they are justified in holding
many moral beliefs, such as that it is morally wrong to beat your
opponent senseless with a baseball bat just because she beat you in a
baseball game. People also claim moral knowledge, such as when a
neighbor says, "I know that it is wrong for him to spank his daughter
so hard, but I don't know what I should do about it." Moral
skepticism conflicts with these common ways of talking and thinking,
so moral skeptics seem to owe us some argument for their controversial claim.




Dogmatic moral skepticism is, moreover, a universal and abstruse claim. It is
the claim that all moral beliefs have a certain epistemic status.
Normally one should not make such a strong claim without some reason.
One should not, for example, claim that all astronomical beliefs are
unjustified unless one has some reason for this claim. Analogously,
it seems that one should not claim that all moral beliefs are
unjustified unless one has some positive argument. Thus, its form,
like its conflict with common sense, seems to create a presumption
against moral skepticism.




Moral skeptics, in response, sometimes try to shift the burden of
proof to their opponents. Anyone who makes the positive moral claim
that sodomy is morally wrong seems to need some reason for
that claim, just as someone who claims that there is life on Mars
seems to need evidence for that claim. If the presumption is always
against those who make positive moral claims, then it is opponents of
moral skepticism who must carry the burden of proof. Or, at least,
moral skeptics can deny that the burden of proof is on moral
skeptics. Then moral skeptics may criticize any moral belief or
theory without needing to offer any positive argument for moral
skepticism, and their opponents need to take moral skepticism
seriously enough to argue against it (cf. Copp 1991).




This controversy about burden of proof might be resolved by
distinguishing dogmatic moral skepticism from Pyrrhonian moral
skepticism. Dogmatic skeptics about justified moral belief
make a universal claim that conflicts with common sense, so they seem
to have the burden of arguing for their claim. In contrast,
Pyrrhonian moral skeptics neither make nor deny any claim about the
epistemic status of any moral belief. They simply raise doubts about
whether moral beliefs are ever justified. This difference suggests
that Pyrrhonian moral skeptics do not take on any or as much burden of proof
as do dogmatic skeptics about justified moral belief.


## 3. Arguments for Moral Skepticism




Whether or not they need to, moral skeptics do offer a variety of
arguments for their position. Here I will focus on arguments for
dogmatic skepticism about justified moral belief, but
essentially the same arguments could be formulated to support dogmatic
skepticism about moral knowledge. I will return later to Pyrrhonian
moral skepticism in section 4. Also, although here I will sometimes formulate these
arguments in terms of moral truth for simplicity, they could be restated in ways more
congenial to skeptics about moral truth-aptness.


### 3.1 Moral Disagreements




The simplest and most common argument for moral skepticism is based
on observed facts: Smart and well-meaning people disagree about the
moral permissibility of abortion, affirmative action, capital
punishment, active euthanasia, nuclear deterrence, welfare reform,
civil rights, and so on. Many observers generalize to the conclusion
that no moral claim is or would be accepted by everyone.


 However, all of these disagreements together still do not exclude
the possibility of agreement on other moral beliefs. Maybe nobody
denies that it is morally wrong to torture babies just to get sexual
pleasure. Moreover, even if no moral belief is immune to disagreement,
the fact that some people disagree with me does not prove that I am
unjustified in holding my moral belief. I might be able to show them
that I am right, or they might agree with me under ideal
circumstances, where they are better informed, more thoughtful, less
partial, and so on. Moral disagreements that are resolvable do not
support moral skepticism, so any argument for moral skepticism from
moral disagreement must show that moral disagreements are unresolvable
on every issue. That will require a separate argument. (For further
discussions, see Bergmann & Kain 2014, Besong 2014, and Vavova
2014.) 


### 3.2 Moral Explanations




Another way to argue for moral skepticism is to cite a requirement on
justified belief. On one view, we cannot be justified in believing any
claim unless the truth of that claim is necessary for the best
explanation of some independent fact. Some philosophers then argue
that moral truths are never necessary for the best explanation of any
non-moral fact (cf. Harman 1977). It follows that we cannot be
justified in believing any moral claim (cf. Hill 2016).




This argument can be countered in two ways. First, one could deny
that justified belief must always involve inference to the best
explanation. It is not clear, for example, that beliefs about
mathematics or colors are or must be grounded in this way, although
such beliefs still seem justified. (Compare Harman 1977 on
mathematics and color.)




Another common response is that sometimes a moral truth is necessary
for the best explanation of a non-moral fact (cf. Sturgeon 1985).
Hitler's vices are sometimes cited to explain his atrocities.
Slavery's injustice has been said to explain its demise. And the
fact that everyone agrees that it is morally wrong to torture babies
just to get sexual pleasure might be best explained by the fact that
this common belief is true.




Moral skeptics usually reply that such explanations can be replaced
by non-moral descriptions of Hitler, slavery, and torture. If such
replacements are always available, then moral truths are not
necessary for the best explanation of anything. However, it is not
clear whether or not non-moral explanations really do work as well as
moral explanations in all cases. Nor is it clear whether inference to
the best explanation must lie behind all justified belief.



A special case of this argument, called an evolutionary debunking
argument, has led to vigorous debate recently (cf. Kahane 2011, May 2018). 
Some moral skeptics (or
at least skeptics about moral realism) argue that moral beliefs can be
explained by evolutionary biology perhaps with help from psychology,
sociology, or culture without appeal to any moral fact or truth. Such
truth-independent explanations are then supposed to show that moral
beliefs are either not true, not really (mind independently) true, or
not justified (cf. Joyce 2006, Street 2006, Braddock 2017). As
with other arguments from the explanatory impotence of moral facts,
critics can reply either by arguing that moral facts do some
explanatory work (e.g. Copp 2008 with reply by Street 2008) or by
arguing that moral beliefs can be justified even if moral facts do not
do any explanatory work (cf. Bergmann & Kain 2014).


### 3.3 A Regress




The next argument develops a skeptical regress. This form of argument,
which derives from Sextus Empiricus (*Outlines of Scepticism*),
is sometimes used to support the more general skeptical claim that no
belief about any topic is justified. Nonetheless, it might seem to
have special force within morality if supposedly foundational moral
beliefs are especially problematic in some way.




The argument's goal is to rule out all of the ways in which a
person might be justified in believing something. It starts with a
definition:



A person *S* is *inferentially* justified in believing
a claim that *p* if and only if what makes *S* justified
is (at least in part) *S*'s ability to infer *p*
from some belief of *S*.





Notice that what matters for this way of being justified is not whether the person *actually* bases the moral belief on an occurrent inference but only whether the person is *able* to infer that moral belief. This ability is usually understood to be present when the person has other beliefs that fit into a structure that the person could use to infer the moral belief.




There are, then, only two ways to be justified:



(1) If any person *S* is justified in believing any moral
claim that *p*, then *S* must be justified either
inferentially or non-inferentially.





The moral skeptic denies both possibilities in turn. First:



(2) No person *S* is ever non-inferentially justified in
believing any moral claim that *p*.





Moral intuitionists and some moral contextualists deny premise (2),
but moral skeptics argue that too many beliefs would be justified if
people did not need to be able to provide any reason or inference to support their moral
beliefs. If Thelma could be non-inferentially justified in believing
that eating meat *is* morally wrong, then Louise could also be
non-inferentially justified in believing that eating meat is
*not* morally wrong, and Nick could be non-inferentially justified in
believing that it is morally wrong to eat vegetables. Conflicting
beliefs can sometimes both be justified, but it seems less plausible
to hold that such conflicting moral beliefs are all justified without
any ability to support the belief with any inference when each believer knows that other people disagree. If
such conflicting beliefs are not justified in the absence of a
reason, and if such conflicts are pervasive enough to undermine all
non-inferential justification, then premise (2) is true.




Another way to argue for premise (2) invokes science. Psychologists
have found that many moral judgments are subject to a variety of
distorting influences, including framing effects and certain
misleading emotions. Biologists then suggest that moral judgments
evolved in ways that seem independent of their truth. Such indications
of unreliability are supposed to show that moral judgments are not
justified without inference (Sinnott-Armstrong 2006, Chapter 9,
pp. 184-219; but see replies by Beaulieu 2009, van Roojen
2013, and May 2018). That would support premise (2).



 Premises (1) and (2) together imply an intermediate conclusion:



(3) If any person *S* is justified in believing any moral
claim that *p*, then *S* must be justified
inferentially.





This means that, to be justified, *S* must be able to infer
*p* from some other beliefs held by *S*. 
Of course, *S* does not have to draw any actual inference, 
but *S* still needs to hold some other beliefs that could be used to justify that belief. 




But which
other beliefs? There are three main possibilities:



(4) If any person *S* is inferentially justified in believing
any moral claim that *p*, then S must be justified by an
inference with either (a) no normative premises or (b) some normative
premises but no moral premises or (c) some moral premises.





To the first possibility, moral skeptics respond with a variation on
the maxim that you can't get "ought" from "is":



(5) No person *S* is ever justified in believing any moral
claim that *p* by an inference with no normative premises.





Naturalists in moral epistemology deny (5) when they try to derive a
conclusion that an act is morally wrong from purely non-normative
features of the act. However, moral skeptics retort that such
derivations always depend on a suppressed premise that all acts with
those features are morally wrong. Such a suppressed premise seems
moral and, hence, normative. If so, the naturalist's inference
does not really work without any normative premises. Naturalists
still might invoke inferences to the best moral explanation, but then
moral skeptics can deny that any moral hypothesis provides the best
explanation independently of prior moral assumptions (see above).




The next possibility is to justify a moral conclusion with an
inference whose premises are not moral but are normative in another
way. This approach, which is adopted by contractarians among others,
can be called *normativism*. Normativists usually start with
premises about rationality and impartiality that are each supposed to
be normative but morally neutral. If rational impartial people under
relevant circumstances would agree to certain moral standards, this
is supposed to show that the corresponding moral beliefs are true or
justified.




One problem for this general approach is that different theories of
rationality, impartiality, and relevant circumstances are all
questionable and lead to contrary moral beliefs. This suggests that
such theories are not morally neutral, so these derivations do not
avoid moral premises. Other arguments from non-moral norms to moral
conclusions run into similar problems. Moral skeptics conclude
that:



(6) No person *S* is ever justified in believing any moral
claim that *p* by an inference with some normative premises but
no moral premises.





Premises (4)-(6) imply another intermediate conclusion:



(7) If any person *S* is justified in believing any moral
claim that *p*, then *S* must be justified by an
inference with some moral premise.





In short, moral beliefs must be justified by moral beliefs.




This creates a problem. Although the justifying beliefs must include
some moral beliefs, not just any moral beliefs will do:



(8) No person *S* is ever justified in believing a moral
claim that *p* by an inference with a moral premise unless
*S* is also justified in believing that moral premise
itself.





Premise (8) is denied by some contextualists, who claim that, even
if a moral belief is not justified, if it is shared within a certain
social context, then it may be used to justify other moral beliefs (cf. Wellman 1971, Timmons 1999).
However, moral skeptics reply that social contexts are often corrupt,
and no social context by itself can show that a moral belief is true,
reliable, or, hence, justified in the relevant way.




But then how can moral premises be justified? Given (7)-(8), the
moral premises must be justified by inferring them from still other
moral beliefs which must also be justified by inferring them from still
other moral beliefs, and so on. To justify a moral belief thus requires
a chain (or branching tree) of justifying beliefs or premises, which must
have one of two forms:



(9) If any person *S* is justified in believing any moral
claim that *p*, then *S* must be justified by a chain of
inferences that either goes on infinitely or circles back to include
*p* itself as an essential premise.





The first of these two alternatives is almost never defended, since
most accept:



(10) No person *S* is ever justified in believing any moral
claim that *p* by a chain of inferences that goes on
infinitely.





Moral skeptics also deny the other possibility:



(11) No person *S* is ever justified in believing any moral
claim that *p* by a chain of inferences that includes *p*
as an essential premise.





Any argument that includes its conclusion as a premise will be
valid. However, anyone who doubts the conclusion will have just as much
reason to doubt the premise. So, according to skeptics, nothing is
gained when a premise just restates the belief to be justified.




Premise (11) is opposed by moral coherentists (e.g. Brink 1989, Sayre-McCord 1996, 
Sinnott-Armstrong 2006, Chapter 10, pp. 220-251). Recent coherentists
emphasize that they do not infer a belief from itself in a linear way.
Instead, a moral belief is supposed to be justified because it coheres
in some way with a body of beliefs that is coherent in some
way. Still, moral skeptics deny that coherence is enough to make a
moral belief justified. One reason is that the internal coherence of a
set of beliefs is not evidence of any relation to anything outside the
beliefs. Another reason is that every belief -- no matter how
ridiculous -- can cohere with some body of beliefs that is
internally coherent. Because so many incompatible systems seem
coherent, moral skeptics deny that coherence alone is sufficient to
make beliefs justified.




Now the moral skeptic can draw a final conclusion. (9)-(11)
imply:



 (12) No person is ever justified in believing any moral
claim.





This is dogmatic skepticism about justified moral beliefs.




Many opponents find this conclusion implausible, but the regress
argument is valid. Hence, its conclusion cannot be avoided without
denying one of its premises. Different opponents of moral skepticism
deny different premises, as indicated. However, it remains to be
seen whether any of these responses to the regress argument is
defensible in the end.


### 3.4 Skeptical Hypotheses




The final kind of argument derives from Rene Descartes
(1641). I do not seem justified in believing that what I see is a
lake if I cannot rule out the possibility that it is a bay or a
bayou. Generalizing, if there is any contrary hypothesis that I
cannot rule out, then I am not justified in believing that what I see
is a lake. This is supposed to be a common standard for justified
belief. When this principle is applied thoroughly, it leads to
skepticism. All a skeptic needs to show is that, for each belief,
there is some contrary hypothesis that cannot be ruled out. It need
not be the same hypothesis for every belief, but skeptics usually buy
wholesale instead of retail, so they seek a single hypothesis that is
contrary to all (or many common) beliefs and which cannot be ruled
out in any way.




The famous Cartesian hypothesis is of a demon who deceives me in all
of my beliefs about the external world, while also ensuring that my
beliefs are completely coherent. This possibility cannot be ruled out
by any experiences or beliefs, because of how the deceiving demon is
defined. This hypothesis is also contrary to my beliefs about the
lake. So my beliefs about the lake are not justified, according to
the above principle. And there is nothing special about my beliefs
about the lake. Everything I believe about the external world is
incompatible with the deceiving demon hypothesis. Skeptics conclude
that no such belief is justified.




This argument is often dismissed on the grounds that there is no
reason to believe in a deceiving demon or that nobody really doubts
whether there is an external world. In contrast, this form of argument is not subject to such objections when it is applied to morality, because some people really do
adopt and even argue for a parallel skeptical hypothesis in
morality:



 Moral Nihilism = Nothing is morally wrong.





Moral nihilism here is not about what is semantically or
metaphysically possible. It is just a substantive, negative,
existential claim that there does not exist anything that is morally
wrong. It is, however, usually supplemented with an explanation of why
people hold moral beliefs that are false (just as the story of
Descartes's deceiving demon is supposed to explain why our perceptual
beliefs are false). This thesis of moral nihilism has been supported
by various reasons, including the pervasiveness of moral disagreement
and our supposed ability (with the help of sociobiology and other
sciences) to explain moral beliefs without reference to moral
facts. Since people do take moral nihilism seriously and even argue
for it (Mackie 1977, Joyce 2001), moral nihilism cannot be dismissed
as readily as Descartes's deceiving demon.




Moral skeptics can then argue that the definition of moral nihilism
forestalls any refutation. Since moral nihilists question all of our
beliefs in moral wrongness, they leave us with no starting points on
which to base arguments against them without begging the question at
issue. Moreover, moral nihilists' explanations of our moral beliefs
predict that we would hold exactly these moral beliefs, so the truth
of its predictions can hardly refute moral nihilism. If this trick
works, then it fits right into a skeptical hypothesis argument.




This argument is clearest when applied to an example. If nothing is
morally wrong, as moral nihilists claim, then it is not morally wrong
to torture babies just for fun. So, according to the general principle
above, one must be able to rule out moral nihilism in order to be
justified in believing that torturing babies just for fun is morally
wrong. Moral skeptics conclude that this moral belief is not
justified. More precisely:




(1) I am not justified in believing the denial of moral nihilism.




(2) I am justified in believing that [(*p*) "It is morally wrong
to torture babies just for fun" entails (*q*) the denial of
moral nihilism].




(3) If I am justified in believing that *p*, and I am justified
in believing that *p* entails *q*, then I am justified
in believing that *q*.




(4) Therefore, I am not justified in believing that it is morally
wrong to torture babies just for fun.





This moral belief is not especially problematic in any way. It seems
as obvious as any moral belief. So the argument can be generalized to
cover any moral belief. Moral skeptics conclude that no moral belief
is justified.




There are two main responses to such skeptical hypothesis arguments
(cf. May 2013). First, some anti-skeptics deny (1) and claim that
skeptical hypotheses can be ruled out somehow. They might argue that
moral nihilism is internally inconsistent or meaningless. If so, it
can be ruled out by logic and semantics alone. However, moral nihilism
does seem consistent and meaningful, according to all plausible
theories of moral language, including expressivism, realism, and
constructivism (Sinnott-Armstrong 2006, chap. 3). Moral nihilism is
also not subject to the kind of argument that Putnam (1981) deploys
against more general skeptical scenarios. Anti-skeptics still might
argue that moral nihilism is incompatible with some non-moral facts or
observations or their best explanations. If so, it can be ruled out by
arguments with only non-moral premises. However, all such attempts to
cross the dreaded is-ought gap are questionable (Sinnott-Armstrong
2006, chaps. 7-8). A third way to rule out moral nihilism would be
based on common moral beliefs that are incompatible with moral
nihilism. However, just as it would beg the question to use common
beliefs about the external world to rule out a deceiving demon
hypothesis, so it would also beg the question to argue against moral
nihilism on the basis of common moral beliefs -- no matter how
obvious those beliefs might seem to us, and no matter how well these
common beliefs cohere together (Sinnott-Armstrong 2006,
chaps. 9-10). Moral skeptics conclude that there is no way to rule out
moral nihilism, just as premise (1) claims.




Another recent response is to deny premise (3). This is a principle of
*closure*. Since a belief entails the denial of every contrary
hypothesis, this closure principle in effect says that I cannot be
justified in believing *p* unless I am justified in denying
every hypothesis contrary to *p* -- that is, unless I can
rule out *all* contrary hypotheses. This principle has been
denied by relevant alternative theorists, who claim instead that only
relevant hypotheses need to be ruled out. On this theory, if skeptical
hypotheses are not relevant, then a belief that it is morally wrong to
torture babies just for fun can be justified, even if the believer
cannot rule out moral nihilism.




For this response to have force, however, opponents of moral
skepticism need to say why moral nihilism is irrelevant. It seems
relevant, for the simple reason that it is directly contrary to the
moral belief that is supposed to be justified. Moreover, real people
believe and give reasons to believe in moral nihilism. Some people are
led to moral nihilism by the absence of any defensible theory of
morality. If consequentialism is absurd or incoherent, as some critics
argue, and if deontological restrictions and permissions are
mysterious and unfounded, as their opponents argue, then some people
might believe moral nihilism for reasons similar to those that led
scientists to reject phlogiston. Another basis for moral nihilism
cites science. If all of our moral beliefs can be explained by
sociobiology and/or other social sciences without assuming that any
moral belief is true, then some might accept moral nihilism for
reasons similar to those that lead many people to reject witches or
elves. The point is not that such reasons for moral nihilism are
adequate. The point here is only that there is enough prima facie
reason to believe moral nihilism that it cannot be dismissed as
irrelevant on this basis. If moral nihilism is relevant, and if
closure holds for all or at least relevant alternatives, and if moral
nihilism cannot be ruled out in any way, then moral skepticism seems
to follow.


### 3.5 Relations Among the Arguments




These arguments for moral skepticism differ in many ways, but they
seem mutually supportive. One crucial premise in the skeptical
hypothesis argument claims that nothing can rule out moral nihilism.
The best way to support that premise is to criticize each method for
ruling out moral nihilism. That is just one instance of what the
regress argument does more generally. The argument from moral
explanations excludes yet another way to rule out moral nihilism. So,
if these other arguments work, they support a crucial premise in the
skeptical hypothesis argument.




Conversely, one crucial premise in the regress argument claims that no
moral belief can be justified non-inferentially. Another crucial
premise, (8), claims that an inference cannot justify its conclusion
unless its premises are justified. These premises claim, in effect,
that a moral belief needs a certain kind of justification. One way to
establish this need is to point to a contrary possibility that is not
yet ruled out. That is what the skeptical hypothesis argument does.
Another way to confirm this need is to show that the moral belief is
controversial. That is what the argument from moral disagreement does.
Thus, if these other arguments work, they support a crucial premise in
the regress argument.




To skeptics, this mutual support might seem desirable. Anti-skeptics,
however, might object that this mutual support makes the arguments
jointly circular. In the end, the force of the arguments depends on
the defensibility of non-skeptical views in moral epistemology. If
moral intuitionism, coherentism, naturalism, or normativism works to
justify some moral beliefs and/or to rule out moral nihilism, then
this will undermine the crucial premises in the arguments for moral
skepticism. But that remains to be seen.


## 4. Pyrrhonian Moral Skepticism




Although the arguments for moral skepticism are hard to refute, most
people reject their conclusion. This makes it natural to seek some
compromise. Various compromises have been proposed, but here I will
focus on one that extends the Pyrrhonian tradition (cf. DePaul 2009).




This neo-Pyrrhonian position can be explained in terms of contrast
classes, which should be familiar from shopping: Are jumbo shrimp
large? An answer of "Yes" or "No" would be too
simple. Jumbo shrimp are large for shrimp, but they are not large for
edible crustaceans. Analogously, someone can be justified in believing
a claim out of one contrast class, even if the same person is not
justified in believing the same claim out of a different contrast
class. For example, suppose a father sees an animal in a zoo and
believes it to be a zebra. If the father has adequate evidence that
the animal is not a lion or a horse, then the father can be justified
in believing that it is a zebra out of the contrast class {lion,
horse, zebra}. Nonetheless, the father still might not have any
evidence that the animal is not a mule painted to look just like a
zebra. Then the father is not justified in believing that the animal
is a zebra out of the contrast class {lion, horse, zebra, painted
mule}.




The same situation arises with moral beliefs. A father might be
justified in believing that he should tell his children the truth
rather than lying to them, even if the father is not justified in
believing that he should tell his children the truth as opposed to
keeping quiet. Or someone might be justified in favoring Kantian moral
theory over act-utilitarianism, because of counterexamples to
act-utilitarianism, without being justified on that basis in favoring
Kantian moral theory over rule-utilitarianism, if that alternative is
not subject to the same counterexamples.




More generally, we can distinguish two contrast classes:




The *extreme contrast class* for a moral belief that
*p* includes every moral claim that is contrary to *p*,
including moral nihilism.




The *modest contrast class* for a moral belief includes all and only those
contrary moral beliefs that most people would take seriously in an
ordinary discussion.





Since moral nihilism conflicts with many commonsense moral beliefs, most people do not take moral nihilism seriously in ordinary discussions, so the modest contrast class does not include moral
nihilism. Thus, anyone who can rule out all other members of the
modest contrast class but cannot rule out moral nihilism is justified
in believing the moral claim out of the modest contrast class but not
out of the extreme contrast class.




These classes enable us to distinguish two versions of moral
skepticism:




*Skepticism about modestly justified moral belief* is the claim
that nobody is ever justified out of the modest contrast
class in holding any substantive moral belief.



*Skepticism about extremely justified moral belief* is the
claim that nobody is ever justified out of the extreme contrast class
in holding any substantive moral belief.





The latter but not the former follows if nobody can ever rule out
moral nihilism, but some believers sometimes can rule out all other
members of the modest contrast class.




Critics will ask, "If someone is justified out of the modest contrast
class but not out of the extreme contrast class, is this believer just
plain justified (period or without qualification)?" That, of course,
depends on what it means to say that a believer is justified (without
qualification). On one plausible account, to say that a believer is
justified (without qualification) is to say that the believer is
justified out of the *relevant* contrast class. But which
contrast class is relevant when?




Contextualists say that the modest contrast class is relevant in
everyday contexts, such as hospital ethics committees, where it would
be seen as a distraction to discuss moral nihilism. Nonetheless, the
extreme contrast class is said to be relevant in philosophical
contexts, such as philosophy classes where moral nihilism is taken
seriously. This allows contextualists to hold that a doctor in a
hospital ethics committee is justified in believing a moral claim that
a philosophy student with the same evidence would not be justified in
believing.




Problems arise when contexts cross. Consider a philosophy student who
says that the doctor on the ethics committee is not justified in
believing the moral claim. Is the student's contrast class (with moral
nihilism) or the doctor's contrast class (without moral nihilism)
really relevant to the student's judgment about the doctor's belief?
And what if the doctor says that the student really is justified while
in the philosophy class? When epistemic assessments cross contexts in
such ways, sometimes the believer's context seems relevant, but
sometimes the assessor's context seems relevant, so it is hard to see
any basis for claiming that either context or either contrast class
really is the relevant one for assessing whether the believer really
is justified (without qualification).




Such paradoxes lead some 'classy' Pyrrhonian moral
skeptics to deny that any contrast class is ever really relevant. This
denial implies that it is never either true or false that a believer
is justified (without qualification), if such claims presuppose that
some contrast class is really relevant. Alternatively, classy
Pyrrhonian moral skeptics might suspend belief about whether any
contrast class is ever really relevant or not. Such Pyrrhonian moral
skeptics refuse to take any position either way on whether any
believer is justified (without qualification), although they can still
talk about whether someone is justified in believing a moral claim out
of a specified contrast class. Pyrrhonian moral skeptics can then (i)
accept skepticism about extremely justified moral belief but (ii) deny
skepticism about modestly justified moral belief and (iii) refuse to
either assert or deny (dogmatic) skepticism about any moral belief
being justified (without qualification). (See Sinnott-Armstrong 2006,
chap. 6.)




Whether or not this view is finally defensible, the point here is just
that such a Pyrrhonian compromise is available and attractive to those
who want to avoid dogmatic moral skepticism but see no way to
refute it. There are also other possible compromises that combine
different strands in moral skepticism. That is what makes it so
fascinating to study this important group of views.