“Moral Skepticism” names a diverse collection of views that deny orraise doubts about various roles of reason in morality. Differentversions of moral skepticism deny or doubt moral knowledge, justifiedmoral belief, moral truth, moral facts or properties, and reasons tobe moral.

Despite this diversity among the views that get labeled “moralskepticism”, many people have very strong feelings about moralskepticism in general. One large group finds moral skepticism obvious,because they do not see how anyone could have real knowledge of themoral status of anything or how moral facts could fit into a physicalworld. Others see moral skepticism as so absurd that any moral theorycan be refuted merely by showing that it leads to moralskepticism. Don’t you know, they ask, that slavery is morally wrong?Or terrorism? Or child abuse? Skeptics who deny that we have reason tobelieve or obey these moral judgments are seen as misguided anddangerous. The stridency and ease of these charges suggests mutualmisunderstanding, so we need to be more charitable and moreprecise.

• 1. Varieties of Moral Skepticism
• 2. A Presumption against Moral Skepticism?
• 3. Arguments for Moral Skepticism
  • 3.1 Moral Disagreements
  • 3.2 Moral Explanations
  • 3.3 A Regress
  • 3.4 Skeptical Hypotheses
  • 3.5 Relations Among the Arguments
• 4. Pyrrhonian Moral Skepticism
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Varieties of Moral Skepticism

Moral skeptics differ in many ways (cf. Machuca 2017), but they share a common core thatmakes them all moral skeptics. What makes moral skepticismmoral is that it concerns morality rather than othertopics. Moral skeptics might go on to be skeptics about the externalworld or about other minds or about induction or about all beliefs orabout all norms or normative beliefs, but these other skepticisms arenot entailed by moral skepticism alone.

What makes moral skepticsskeptics is that they raise doubtsabout common beliefs. Moral skeptics then differ in the kinds ofcommon beliefs that they doubt. They might, for example, doubtcategorical or absolute moral beliefs without doubting weaker kinds ofmoral beliefs. Moral skeptics also differ in the kinds of doubts thatthey raise. Since general skepticism is an epistemological view aboutthe limits of knowledge or justified belief, the most central versionof moral skepticism is the one that raises doubts about moralknowledge or justified moral belief.

There are two main traditions in epistemological skepticism. Onetradition makes the claim that nobody ever knows or can knowanything. This claim is sometimes namedCartesian skepticism(although Descartes argued against it) orAcademic skepticism(despite other interpretations of skeptics in the ancientAcademy). For lack of a better description, we can callitdogmatic skepticism, because such skeptics dogmaticallyassert a universal claim. In contrast, no such claim is madebyPyrrhonian skeptics. They also don’t deny any claim likethis. They have so much doubt that they refrain from taking anyposition one way or the other on whether anyone does or does not orcan or cannot know anything.

Moral skepticism comes in two corresponding varieties.Pyrrhonianskeptics about moral knowledge refuse to admit that some peoplesometimes know that some substantive moral belief is true. They doubtthat moral knowledge is possible. Still, they do not go on to make theopposite claim that moral knowledge is impossible. They doubt that,too. Their doubts are so extreme that they do not make any claim oneway or the other about the actuality or possibility of moralknowledge. Parallel views can be adopted regarding justified moralbelief.Pyrrhonian skeptics about justified moral beliefsuspend or withhold belief about the actuality or possibility of anyjustified moral belief.

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

Dogmatic skepticism about moral knowledge is the claim that nobodyever knows that any substantive moral belief is true (cf. Butchvarov1989, 2).

Some moral skeptics add this related claim:

Dogmatic skepticism about justified moral belief is the claim thatnobody is ever justified in holding any substantive moral belief.

(The relevant way of being justified is specified inSinnott-Armstrong 2006, chap. 4.) These two claims and Pyrrhonian moralskepticism all fall under the general heading ofepistemologicalmoral skepticism.

The relation between these two claims depends on the nature ofknowledge. If knowledge implies justified belief, as is traditionallysupposed, then skepticism about justified moral belief impliesskepticism about moral knowledge. However, even if knowledge doesrequire justified belief, it does not requireonly justifiedbelief, so skepticism about moral knowledge does not imply skepticismabout justified moral belief.

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

Skepticism about moral truth is the claim that nosubstantive moral belief is true.

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

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 morallanguage 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 “BooKnicks”) or prescriptions for action (such as “GoCeltics”). Such expressions and prescriptions are kinds of thingthat cannot be either true or false. Thus, if these analogies hold inall relevant respects, then substantive moral beliefs are also not theright kind of thing to be either true or false. They are not apt forevaluation in terms of truth. For this reason, such linguistictheories are often taken to imply skepticism about moraltruth-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 ofmoral truth while denying that moral beliefs can be true or false inthe same robust way as factual beliefs.

Such views are often described asnon-cognitivism. That labelis misleading, because etymology suggests that cognitivism is aboutcognition, which is knowledge. Since knowledge implies truth,skepticism about moral truth-aptness has implications for moralknowledge, but it is directly about truth-aptness and not about moralknowledge.

Whatever you call it, skepticism about moral truth-aptness runs intoseveral problems. If moral assertions have no truth-value, then it ishard to see how they can fit into truth-functional contexts, such asnegation, disjunction, and conditionals (Sinnott-Armstrong 2000). Such contexts are alsounassertive, so they do not express the same emotions or prescriptionsas when moral claims are asserted. Indeed, no particular emotion orprescription seems to be expressed when someone says, “Eatingmeat is not morally wrong” (cf. Schroeder 2010). Expressivistsand prescriptivists respond to such objections, but their responsesremain controversial (cf. Sinnott-Armstrong 2006, chap. 2).

Many moral theorists conclude that moral assertions express not onlyemotions or prescriptions but alsobeliefs. In particular,they express beliefs that certain acts, institutions, or people havecertain moral properties (such as moral rightness or wrongness) orbeliefs in moral facts (such as the fact that a certain act is morallyright or wrong). This non-skeptical linguistic analysis still does notshow that such moral claims can be true, since assertions can expressbeliefs that are false or neither true nor false. Indeed, allsubstantive moral assertions and beliefs are false (or neither truenor false) if they claim (or semantically presuppose) moral facts orproperties, and if this metaphysical thesis holds:

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

Skepticism about moral reality is, thus, a reason for skepticism withmoral falsehood, as developed by Mackie (1977), or skepticism aboutmoral truth-value, as developed by Joyce (2001). Opponents ofsucherror theories often object that some moral beliefs mustbe true because some moral beliefs deny the truth of other moralbeliefs. However, error theorists can allow a negative moral belief(such as that eating meat isnot morally wrong) to be true, but only if it merely deniesthe truth of the corresponding positive moral belief (that eating meatis morally wrong). If such denials of moral beliefs are notsubstantive moral beliefs (as denials of astrological beliefs are notastrology), then error theorists can maintain that allsubstantive moral beliefs are false or neither true nor false.

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

Yet another non-epistemological form of moral skepticism answers thequestion “Why be moral?” This question is used to raisemany different issues. Almost everyone admits that thereissometimes some kind of reason to be moral. However, manyphilosophers deny various universal claims, including the claims thatthere isalways some reason to be moral, that there is alwaysa distinctivelymoral (as opposed to self-interested) reason to be moral,and/or that there is alwaysenough reason to make itirrational not to be moral or at least not irrational to be moral.These distinct denials can be seen as separate forms ofpracticalmoral skepticism, which are discussed in more detail in thefollowing supplementary document:

Supplement on Practical Moral Skepticism

Practical moral skepticism resembles epistemological moral skepticismin that both kinds of skepticism deny a role to reasons inmorality. However, epistemological moral skepticism is about reasonsforbelief, whereas practical moral skepticism is aboutreasons foraction. Moreover, practical moral skepticsusually deny that there isalways enough reason for moralaction, whereas epistemological moral skeptics usually deny thatthere isever an adequate reason for moralbelief. Consequently, practical moral skepticism does not implyepistemological moral skepticism. Some moral theorists do assume thata reason to believe that an act is immoral cannot be adequate unlessit also provides a reason not to do that act. However, even if thetwo kinds of reasons are related in this way, they are stilldistinct, so practical moral skepticism must not be confused withepistemological moral skepticism.

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

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

These kinds of moral skepticism can be diagrammed as follows:

Figure 1.

Skepticism about justified moral belief will be the primary topic forthe rest of this entry, and I will refer to it henceforth simply asmoral 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 benice people. They need not be any less motivated to be moral, norneed they have (or believe in) any less reason to be moral thannon-skeptics have (or believe in). Moral skeptics can holdsubstantive moral beliefs just as strongly as non-skeptics. Theirsubstantive moral beliefs can be common and plausible ones. Moralskeptics can even believe that their moral beliefs are true by virtueof corresponding to an independent moral reality. All that moralskeptics need to deny or doubt in order to be moral skeptics is that their (or anyone’s) moral beliefs arejustified. This meta-ethical position about the epistemic status ofmoral beliefs need not trickle down and infect anyone’ssubstantive moral beliefs or actions.

Critics still argue that moral skepticism conflicts withcommon sense. Most people think that they are justified in holdingmany moral beliefs, such as that it is morally wrong to beat youropponent senseless with a baseball bat just because she beat you in abaseball game. People also claim moral knowledge, such as when aneighbor says, “I know that it is wrong for him to spank his daughterso hard, but I don’t know what I should do about it.” Moralskepticism 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 isthe 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 areunjustified unless one has some reason for this claim. Analogously,it seems that one should not claim that all moral beliefs areunjustified unless one has some positive argument. Thus, its form,like its conflict with common sense, seems to create a presumptionagainst moral skepticism.

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

This controversy about burden of proof might be resolved bydistinguishing dogmatic moral skepticism from Pyrrhonian moralskepticism. Dogmatic skeptics about justified moral beliefmake a universal claim that conflicts with common sense, so they seemto have the burden of arguing for their claim. In contrast,Pyrrhonian moral skeptics neither make nor deny any claim about theepistemic status of any moral belief. They simply raise doubts aboutwhether moral beliefs are ever justified. This difference suggeststhat Pyrrhonian moral skeptics do not take on any or as much burden of proofas do dogmatic skeptics about justified moral belief.

3. Arguments for Moral Skepticism

Whether or not they need to, moral skeptics do offer a variety ofarguments for their position. Here I will focus on arguments fordogmatic skepticism about justified moral belief, butessentially the same arguments could be formulated to support dogmaticskepticism about moral knowledge. I will return later to Pyrrhonianmoral skepticism in section 4. Also, although here I will sometimes formulate thesearguments in terms of moral truth for simplicity, they could be restated in ways morecongenial to skeptics about moral truth-aptness.

3.1 Moral Disagreements

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

However, all of these disagreements together still do not excludethe possibility of agreement on other moral beliefs. Maybe nobodydenies that it is morally wrong to torture babies just to get sexualpleasure. Moreover, even if no moral belief is immune to disagreement,the fact that some people disagree with me does not prove that I amunjustified in holding my moral belief. I might be able to show themthat I am right, or they might agree with me under idealcircumstances, where they are better informed, more thoughtful, lesspartial, and so on. Moral disagreements that are resolvable do notsupport moral skepticism, so any argument for moral skepticism frommoral disagreement must show that moral disagreements are unresolvableon every issue. That will require a separate argument. (For furtherdiscussions, see Bergmann & Kain 2014, Besong 2014, and Vavova2014.)

3.2 Moral Explanations

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

This argument can be countered in two ways. First, one could denythat justified belief must always involve inference to the bestexplanation. It is not clear, for example, that beliefs aboutmathematics or colors are or must be grounded in this way, althoughsuch beliefs still seem justified. (Compare Harman 1977 onmathematics and color.)

Another common response is that sometimes a moral truth is necessaryfor 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 thefact that everyone agrees that it is morally wrong to torture babiesjust to get sexual pleasure might be best explained by the fact thatthis common belief is true.

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

A special case of this argument, called an evolutionary debunkingargument, has led to vigorous debate recently (cf. Kahane 2011, May 2018). Some moral skeptics (orat least skeptics about moral realism) argue that moral beliefs can beexplained by evolutionary biology perhaps with help from psychology,sociology, or culture without appeal to any moral fact or truth. Suchtruth-independent explanations are then supposed to show that moralbeliefs are either not true, not really (mind independently) true, ornot justified (cf. Joyce 2006, Street 2006, Braddock 2017). Aswith other arguments from the explanatory impotence of moral facts,critics can reply either by arguing that moral facts do someexplanatory work (e.g. Copp 2008 with reply by Street 2008) or byarguing that moral beliefs can be justified even if moral facts do notdo 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 nobelief about any topic is justified. Nonetheless, it might seem tohave special force within morality if supposedly foundational moralbeliefs are especially problematic in some way.

The argument’s goal is to rule out all of the ways in which aperson might be justified in believing something. It starts with adefinition:

A personS isinferentially justified in believinga claim thatp if and only if what makesS justifiedis (at least in part)S’s ability to inferpfrom some belief ofS.

Notice that what matters for this way of being justified is not whether the personactually bases the moral belief on an occurrent inference but only whether the person isable 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 personS is justified in believing any moralclaim thatp, thenS must be justified eitherinferentially or non-inferentially.

The moral skeptic denies both possibilities in turn. First:

(2) No personS is ever non-inferentially justified inbelieving any moral claim thatp.

Moral intuitionists and some moral contextualists deny premise (2),but moral skeptics argue that too many beliefs would be justified ifpeople did not need to be able to provide any reason or inference to support their moralbeliefs. If Thelma could be non-inferentially justified in believingthat eating meatis morally wrong, then Louise could also benon-inferentially justified in believing that eating meat isnot morally wrong, and Nick could be non-inferentially justified inbelieving that it is morally wrong to eat vegetables. Conflictingbeliefs can sometimes both be justified, but it seems less plausibleto hold that such conflicting moral beliefs are all justified withoutany ability to support the belief with any inference when each believer knows that other people disagree. Ifsuch conflicting beliefs are not justified in the absence of areason, and if such conflicts are pervasive enough to undermine allnon-inferential justification, then premise (2) is true.

Another way to argue for premise (2) invokes science. Psychologistshave found that many moral judgments are subject to a variety ofdistorting influences, including framing effects and certainmisleading emotions. Biologists then suggest that moral judgmentsevolved in ways that seem independent of their truth. Such indicationsof unreliability are supposed to show that moral judgments are notjustified without inference (Sinnott-Armstrong 2006, Chapter 9,pp. 184–219; but see replies by Beaulieu 2009, van Roojen2013, and May 2018). That would support premise (2).

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

(3) If any personS is justified in believing any moralclaim thatp, thenS must be justifiedinferentially.

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

But whichother beliefs? There are three main possibilities:

(4) If any personS is inferentially justified in believingany moral claim thatp, then S must be justified by aninference with either (a) no normative premises or (b) some normativepremises but no moral premises or (c) some moral premises.

To the first possibility, moral skeptics respond with a variation onthe maxim that you can’t get “ought” from “is”:

(5) No personS is ever justified in believing any moralclaim thatp by an inference with no normative premises.

Naturalists in moral epistemology deny (5) when they try to derive aconclusion that an act is morally wrong from purely non-normativefeatures of the act. However, moral skeptics retort that suchderivations always depend on a suppressed premise that all acts withthose features are morally wrong. Such a suppressed premise seemsmoral and, hence, normative. If so, the naturalist’s inferencedoes not really work without any normative premises. Naturalistsstill might invoke inferences to the best moral explanation, but thenmoral skeptics can deny that any moral hypothesis provides the bestexplanation independently of prior moral assumptions (see above).

The next possibility is to justify a moral conclusion with aninference whose premises are not moral but are normative in anotherway. This approach, which is adopted by contractarians among others,can be callednormativism. Normativists usually start withpremises about rationality and impartiality that are each supposed tobe normative but morally neutral. If rational impartial people underrelevant circumstances would agree to certain moral standards, thisis supposed to show that the corresponding moral beliefs are true orjustified.

One problem for this general approach is that different theories ofrationality, impartiality, and relevant circumstances are allquestionable and lead to contrary moral beliefs. This suggests thatsuch theories are not morally neutral, so these derivations do notavoid moral premises. Other arguments from non-moral norms to moralconclusions run into similar problems. Moral skeptics concludethat:

(6) No personS is ever justified in believing any moralclaim thatp by an inference with some normative premises butno moral premises.

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

(7) If any personS is justified in believing any moralclaim thatp, thenS must be justified by aninference with some moral premise.

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

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

(8) No personS is ever justified in believing a moralclaim thatp by an inference with a moral premise unlessS is also justified in believing that moral premiseitself.

Premise (8) is denied by some contextualists, who claim that, evenif a moral belief is not justified, if it is shared within a certainsocial 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), themoral premises must be justified by inferring them from still othermoral beliefs which must also be justified by inferring them from stillother moral beliefs, and so on. To justify a moral belief thus requiresa chain (or branching tree) of justifying beliefs or premises, which musthave one of two forms:

(9) If any personS is justified in believing any moralclaim thatp, thenS must be justified by a chain ofinferences that either goes on infinitely or circles back to includep itself as an essential premise.

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

(10) No personS is ever justified in believing any moralclaim thatp by a chain of inferences that goes oninfinitely.

Moral skeptics also deny the other possibility:

(11) No personS is ever justified in believing any moralclaim thatp by a chain of inferences that includespas an essential premise.

Any argument that includes its conclusion as a premise will bevalid. However, anyone who doubts the conclusion will have just as muchreason to doubt the premise. So, according to skeptics, nothing isgained 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 coherentistsemphasize that they do not infer a belief from itself in a linear way.Instead, a moral belief is supposed to be justified because it coheresin some way with a body of beliefs that is coherent in someway. Still, moral skeptics deny that coherence is enough to make amoral belief justified. One reason is that the internal coherence of aset of beliefs is not evidence of any relation to anything outside thebeliefs. Another reason is that every belief — no matter howridiculous — can cohere with some body of beliefs that isinternally coherent. Because so many incompatible systems seemcoherent, moral skeptics deny that coherence alone is sufficient tomake beliefs justified.

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

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

This is dogmatic skepticism about justified moral beliefs.

Many opponents find this conclusion implausible, but the regressargument is valid. Hence, its conclusion cannot be avoided withoutdenying one of its premises. Different opponents of moral skepticismdeny different premises, as indicated. However, it remains to beseen whether any of these responses to the regress argument isdefensible in the end.

3.4 Skeptical Hypotheses

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

The famous Cartesian hypothesis is of a demon who deceives me in allof my beliefs about the external world, while also ensuring that mybeliefs are completely coherent. This possibility cannot be ruled outby any experiences or beliefs, because of how the deceiving demon isdefined. This hypothesis is also contrary to my beliefs about thelake. So my beliefs about the lake are not justified, according tothe above principle. And there is nothing special about my beliefsabout the lake. Everything I believe about the external world isincompatible with the deceiving demon hypothesis. Skeptics concludethat no such belief is justified.

This argument is often dismissed on the grounds that there is noreason to believe in a deceiving demon or that nobody really doubtswhether 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 doadopt and even argue for a parallel skeptical hypothesis inmorality:

Moral Nihilism = Nothing is morally wrong.

Moral nihilism here is not about what is semantically ormetaphysically possible. It is just a substantive, negative,existential claim that there does not exist anything that is morallywrong. It is, however, usually supplemented with an explanation of whypeople hold moral beliefs that are false (just as the story ofDescartes’s deceiving demon is supposed to explain why our perceptualbeliefs are false). This thesis of moral nihilism has been supportedby various reasons, including the pervasiveness of moral disagreementand our supposed ability (with the help of sociobiology and othersciences) to explain moral beliefs without reference to moralfacts. Since people do take moral nihilism seriously and even arguefor it (Mackie 1977, Joyce 2001), moral nihilism cannot be dismissedas readily as Descartes’s deceiving demon.

Moral skeptics can then argue that the definition of moral nihilismforestalls any refutation. Since moral nihilists question all of ourbeliefs in moral wrongness, they leave us with no starting points onwhich to base arguments against them without begging the question atissue. Moreover, moral nihilists’ explanations of our moral beliefspredict that we would hold exactly these moral beliefs, so the truthof its predictions can hardly refute moral nihilism. If this trickworks, then it fits right into a skeptical hypothesis argument.

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

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

There are two main responses to such skeptical hypothesis arguments(cf. May 2013). First, some anti-skeptics deny (1) and claim thatskeptical hypotheses can be ruled out somehow. They might argue thatmoral nihilism is internally inconsistent or meaningless. If so, itcan be ruled out by logic and semantics alone. However, moral nihilismdoes seem consistent and meaningful, according to all plausibletheories of moral language, including expressivism, realism, andconstructivism (Sinnott-Armstrong 2006, chap. 3). Moral nihilism isalso not subject to the kind of argument that Putnam (1981) deploysagainst more general skeptical scenarios. Anti-skeptics still mightargue that moral nihilism is incompatible with some non-moral facts orobservations or their best explanations. If so, it can be ruled out byarguments with only non-moral premises. However, all such attempts tocross the dreaded is-ought gap are questionable (Sinnott-Armstrong2006, chaps. 7–8). A third way to rule out moral nihilism would bebased on common moral beliefs that are incompatible with moralnihilism. However, just as it would beg the question to use commonbeliefs about the external world to rule out a deceiving demonhypothesis, so it would also beg the question to argue against moralnihilism on the basis of common moral beliefs — no matter howobvious those beliefs might seem to us, and no matter how well thesecommon beliefs cohere together (Sinnott-Armstrong 2006,chaps. 9–10). Moral skeptics conclude that there is no way to rule outmoral nihilism, just as premise (1) claims.

Another recent response is to deny premise (3). This is a principle ofclosure. Since a belief entails the denial of every contraryhypothesis, this closure principle in effect says that I cannot bejustified in believingp unless I am justified in denyingevery hypothesis contrary top — that is, unless I canrule outall contrary hypotheses. This principle has beendenied by relevant alternative theorists, who claim instead that onlyrelevant hypotheses need to be ruled out. On this theory, if skepticalhypotheses are not relevant, then a belief that it is morally wrong totorture babies just for fun can be justified, even if the believercannot rule out moral nihilism.

For this response to have force, however, opponents of moralskepticism need to say why moral nihilism is irrelevant. It seemsrelevant, for the simple reason that it is directly contrary to themoral belief that is supposed to be justified. Moreover, real peoplebelieve and give reasons to believe in moral nihilism. Some people areled to moral nihilism by the absence of any defensible theory ofmorality. If consequentialism is absurd or incoherent, as some criticsargue, and if deontological restrictions and permissions aremysterious and unfounded, as their opponents argue, then some peoplemight believe moral nihilism for reasons similar to those that ledscientists to reject phlogiston. Another basis for moral nihilismcites science. If all of our moral beliefs can be explained bysociobiology and/or other social sciences without assuming that anymoral belief is true, then some might accept moral nihilism forreasons similar to those that lead many people to reject witches orelves. The point is not that such reasons for moral nihilism areadequate. The point here is only that there is enough prima faciereason to believe moral nihilism that it cannot be dismissed asirrelevant on this basis. If moral nihilism is relevant, and ifclosure holds for all or at least relevant alternatives, and if moralnihilism cannot be ruled out in any way, then moral skepticism seemsto follow.

3.5 Relations Among the Arguments

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

Conversely, one crucial premise in the regress argument claims that nomoral belief can be justified non-inferentially. Another crucialpremise, (8), claims that an inference cannot justify its conclusionunless its premises are justified. These premises claim, in effect,that a moral belief needs a certain kind of justification. One way toestablish this need is to point to a contrary possibility that is notyet ruled out. That is what the skeptical hypothesis argument does.Another way to confirm this need is to show that the moral belief iscontroversial. That is what the argument from moral disagreement does.Thus, if these other arguments work, they support a crucial premise inthe regress argument.

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

4. Pyrrhonian Moral Skepticism

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

This neo-Pyrrhonian position can be explained in terms of contrastclasses, which should be familiar from shopping: Are jumbo shrimplarge? An answer of “Yes” or “No” would be toosimple. Jumbo shrimp are large for shrimp, but they are not large foredible crustaceans. Analogously, someone can be justified in believinga claim out of one contrast class, even if the same person is notjustified in believing the same claim out of a different contrastclass. For example, suppose a father sees an animal in a zoo andbelieves it to be a zebra. If the father has adequate evidence thatthe animal is not a lion or a horse, then the father can be justifiedin believing that it is a zebra out of the contrast class {lion,horse, zebra}. Nonetheless, the father still might not have anyevidence that the animal is not a mule painted to look just like azebra. Then the father is not justified in believing that the animalis a zebra out of the contrast class {lion, horse, zebra, paintedmule}.

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

More generally, we can distinguish two contrast classes:

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 moralnihilism. Thus, anyone who can rule out all other members of themodest contrast class but cannot rule out moral nihilism is justifiedin believing the moral claim out of the modest contrast class but notout of the extreme contrast class.

These classes enable us to distinguish two versions of moralskepticism:

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

Critics will ask, “If someone is justified out of the modest contrastclass but not out of the extreme contrast class, is this believer justplain justified (period or without qualification)?” That, of course,depends on what it means to say that a believer is justified (withoutqualification). On one plausible account, to say that a believer isjustified (without qualification) is to say that the believer isjustified out of therelevant contrast class. But whichcontrast class is relevant when?

Contextualists say that the modest contrast class is relevant ineveryday contexts, such as hospital ethics committees, where it wouldbe seen as a distraction to discuss moral nihilism. Nonetheless, theextreme contrast class is said to be relevant in philosophicalcontexts, such as philosophy classes where moral nihilism is takenseriously. This allows contextualists to hold that a doctor in ahospital ethics committee is justified in believing a moral claim thata philosophy student with the same evidence would not be justified inbelieving.

Problems arise when contexts cross. Consider a philosophy student whosays that the doctor on the ethics committee is not justified inbelieving the moral claim. Is the student’s contrast class (with moralnihilism) 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 whilein the philosophy class? When epistemic assessments cross contexts insuch ways, sometimes the believer’s context seems relevant, butsometimes the assessor’s context seems relevant, so it is hard to seeany basis for claiming that either context or either contrast classreally is the relevant one for assessing whether the believer reallyis justified (without qualification).

Such paradoxes lead some ‘classy’ Pyrrhonian moralskeptics to deny that any contrast class is ever really relevant. Thisdenial implies that it is never either true or false that a believeris justified (without qualification), if such claims presuppose thatsome contrast class is really relevant. Alternatively, classyPyrrhonian moral skeptics might suspend belief about whether anycontrast class is ever really relevant or not. Such Pyrrhonian moralskeptics refuse to take any position either way on whether anybeliever is justified (without qualification), although they can stilltalk about whether someone is justified in believing a moral claim outof a specified contrast class. Pyrrhonian moral skeptics can then (i)accept skepticism about extremely justified moral belief but (ii) denyskepticism about modestly justified moral belief and (iii) refuse toeither assert or deny (dogmatic) skepticism about any moral beliefbeing justified (without qualification). (See Sinnott-Armstrong 2006,chap. 6.)

Whether or not this view is finally defensible, the point here is justthat such a Pyrrhonian compromise is available and attractive to thosewho want to avoid dogmatic moral skepticism but see no way torefute it. There are also other possible compromises that combinedifferent strands in moral skepticism. That is what makes it sofascinating to study this important group of views.

Bibliography

• Ayer, A. J., 1952,Language, Truth, and Logic, New York:Dover. (First edition originally published in 1935.)
• Bambrough, Renford, 1979,Moral Skepticism and MoralKnowledge, London: Routledge.
• Beaulieu, Gerard, 2009, “Sinnott-Armstrong’s MoralSkepticism: A Murdochian Response”,Dialogue, 48(3):673–678.
• Bergmann, Michael, and Kain, Patrick, eds., 2014,Challengesto Moral and Religious Belief: Disagreement and Evolution, NewYork: Oxford University Press.
• Besong, Brian, 2014, “Moral Intuition andDisagreement”,Synthese, 191(12): 2767–2789.
• Blackburn, Simon, 1993,Essays in Quasi-Realism, New York:Oxford University Press.
• Braddock, Matthew, 2017, “Debunking Arguments fromInsensitivity”,International Journal for the Study ofSkepticism, 7(2):91–113.
• Brink, David, 1989,Moral Realism and the Foundations ofEthics, Cambridge: Cambridge University Press.
• Butchvarov, Panayot, 1989,Skepticism in Ethics,Bloomington and Indianapolis; Indiana University Press.
• Copp, David, 1991, “Moral Skepticism”,PhilosophicalStudies, 62: 203–233.
• –––, 2008, “Darwinian Skepticism aboutMoral Realism”,Philosophical Issues, 18: 186–206.
• DePaul, Michael, 2009, “Pyrrhonian Moral Skepticism and theProblem of the Criterion”,Philosophical Issues, 19(1):38–56.
• Descartes, René, 1641,Meditations on FirstPhilosophy, translated by D. C. Cress, Indianapolis: Hackett,1979.
• Gibbard Allan, 1990,Wise Choices, Apt Feeling, Cambridge:Harvard University Press.
• –––, 2003,Thinking How to Live,Cambridge: Harvard University Press.
• Hare, R. M., 1981,Moral Thinking, Oxford: ClarendonPress.
• Harman, Gilbert, 1977,The Nature of Morality, New York:Oxford University Press.
• Hill, Scott, 2016, “From Isolation toSkepticism”,Erkenntnis, 81:649–668.
• Joyce, Richard, 2001,The Myth of Morality, Cambridge:Cambridge University Press.
• –––, 2006,The Evolution of Morality,Cambridge: MIT Press.
• Kahane, Guy, 2011, “Evolutionary Debunking Arguments”,Nous, 45:103–125.
• Machuca, Diego E., ed., 2017,Moral Skepticism: New Essays, NewYork: Routledge.
• Mackie, J. L., 1977,Ethics: Inventing Right and Wrong,New York: Penguin.
• May, Joshua, 2013, “Skeptical Hypotheses and MoralSkepticism”,Canadian Journal of Philosophy, 43(3):341–359.
• –––, 2018,Regard for Reason in the Moral Mind, New York: Oxford University Press.
• Putnam, Hilary, 1981,Reason, Truth, and History,Cambridge: Cambridge University Press.
• Russell, Bruce, 1988, “Two Forms of Ethical Skepticism”, in L.Pojman, ed.,Ethical Theory, Belmont, Cal.: Wadsworth.
• Sayre-McCord, Geoffrey, 1996, “Coherentist Epistemology and Moral Theory”,inMoral Knowledge? New Readings in Moral Epistemology, W. Sinnott-Armstrong and M. Timmons,(eds.), New York: Oxford University Press.
• Schroeder, Mark, 2010,Being For: Evaluating the SemanticProgram of Expressivism, New York: Oxford University Press.
• Sextus Empiricus,Outlines of Scepticism, translatedby Julia Annas and Jonathan Barnes, Cambridge: Cambridge UniversityPress, 2000.
• Shafer-Landau, Russ, 2005,Moral Realism: A Defense, NewYork: Oxford University Press.
• Sidgwick, Henry, 1874/1966,Methods of Ethics, New York:Dover. (First edition originally published in 1874.)
• Singer, Marcus, 1973, “Moral Skepticism”,inSkepticism and Moral Principles, C. Carter (ed.),Evanston, Ill.: New University Press.
• Sinnott-Armstrong, Walter, 2006,Moral Skepticisms, NewYork: Oxford University Press.
• –––, 2010, “Expressivism and Embedding”,Philosophy and Phenomenological Research, 61: 677–693.
• Stevenson, Charles, 1944,Ethics and Language, New Haven:Yale University Press.
• Street, Sharon, 2006, “A Darwinian Dilemma for RealistTheories of Value”,Philosophical Studies, 127:109–166.
• –––, 2008, “Reply to Copp: Naturalism,Normativity, and the Varieties of Realism Worth WorryingAbout”,Philosophical Issues, 18: 207–228.
• Sturgeon, Nicholas, 1985, “Moral Explanations”,inMorality, Reason, and Truth, D. Copp and D. Zimmerman,(eds.), Totowa, N.J.: Rowman and Allanheld.
• Timmons, Mark, 1999,Morality Without Foundations: A Defenseof Ethical Contextualism, New York: Oxford University Press.
• Van Roojen, Mark, 2013, “Moral Intuitionism, Experiments,and Skeptical Arguments”, inIntuitions, Booth andRowbottom, (eds.), Oxford: Oxford University Press.
• Vavova, Katia, 2014, “Moral Disagreement and MoralSkepticism”,Philosophical Perspectives, 28(1):302–333.
• Wellman, Carl, 1971,Challenge and Response: Justification in Ethics, Carbondale: Southern Illinois University Press.
• Williams, Bernard, 1985,Ethics and the Limits ofPhilosophy, Cambridge, MA: Harvard University Press.

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