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DEBUNKING ARGUMENTS 551
The second assumption motivating the intuitionist claim is that morality is autonomous in
two senses. On the one hand, it is logically autonomous, which means that there are no valid,
informative inferences from purely non-moral premises to moral conclusions. This thesis is a
version of the famous ‘is/ought gap’ (cf. Schurz 1997 for a detailed discussion). And on the
other hand, morality is semantically autonomous: we cannot give a convincing reductive
analysis of moral propositions in purely non-moral terms. 5 The thesis of the logical autonomy
of morality is of course widely accepted, but many also agree that morality is semantically
autonomous. (Intuitionism in the minimal sense is not committed to a third version of the
autonomy thesis, namely the claim that morality is metaphysically autonomous.) Anyone
who subscribes to both theses, and who acknowledges that we ‘need to start somewhere’ in
our inquiries, is committed to the intuitionist claim that we have to rely on some moral
intuitions if we are to find justified answers to moral questions.
However, they could still deny that we are in fact justified in any of our moral beliefs. Walter
Sinnott-Armstrong, for example, is an advocate of this view. He accepts that moral justification
is only possible if we rely on moral intuitions at some point. But he defends a form of
epistemic moral scepticism, because he believes that we can never trust our moral intuitions.
And this mistrust of moral intuitions is partly based on his acceptance of certain debunking
arguments (cf. Sinnott-Armstrong 2006: 207-210). Let us now take a closer look at the nature
of such arguments.
3. How Debunking Arguments Can Challenge Moral Intuitionism
Debunking arguments aim at undermining the beliefs they target, in the sense of showing
them to be unjustified or of removing their justification. They do so by providing an allegedly
exhaustive explanation for why the relevant propositions are believed, an explanation that is
(a) independent of the truth or correctness of the beliefs and (b) leaves no room for a justificatory
account of them. The general form of debunking arguments can be put as follows: 6
P1 The best explanation for S’s belief that p is origin or process X.
P2 X has nothing to do with the truth or correctness of p.
C
S’s belief that p is not justified or trustworthy.
Debunking arguments can be formulated both from within internalist and externalist conceptions
of justification. A third premise like “S is in a position to know that P1 and P2 are the
case”, i.e. a premise concerning the access to the undermining factors is needed in internalist
views to warrant the conclusion. By adding a fourth premise such as the following, we could
transform the argument into a deductive one: “When an origin or a process that best explains
a belief has nothing to do with the belief’s correctness or truth, then this belief is not justified
or trustworthy.” For the sake of simplicity, I ignore those modifications here.
Consider the following example as an illustration of the potential force of this type of
argument:
5
Some forms of semantic reductionism actually are compatible with intuitionism insofar as they are
committed to the view that to find an adequate reduction of moral propositions in terms of non-moral
propositions, we need to rely on moral intuitions (cf. Schroeder 2009: 199). Thomas Scanlon’s contractualism,
for example, which proposes that moral judgments be analysed in terms of reasons, is
compatible with the semantic autonomy thesis. This is because the notion of ‘reasonableness’ that
Scanlon uses here is, to use his phrase, “an idea with moral content” (Scanlon 1998: 194; cf. also Parfit
2011: vol., 1 sect. 53).
6
This is a slightly adapted version of Guy Kahane’s analysis of debunking arguments (cf. Kahane 2011:
106).