Of course . . . it will not be sufficient that nihilism be an explanation of the existence and nature of moral disagreement; it must clearly be the best explanation.
The argument from moral diversity or disagreement has been a popular and
philosophically influential source of moral skepticism. Mackie’s “argument from
relativity” is the most perspicuous formulation of the argument from disagreement,
As Mackie recognizes, disagreement does not entail nihilism; we do not infer from
the fact that there are disagreements in the natural or social sciences that these
disciplines do not concern matters of objective fact. Nor, from the fact that there is
a specific dispute in some discipline, do we make what might seem to be the more
modest inference that there is no fact of the matter on the particular issue in question.
For example, no one concluded from the apparently quite deep disagreement among
astronomers a short while ago about the existence of black holes that there was no