Morality and Mathematics: Can You Be A Moral Antirealist and a Mathematical Realist?

716px-EuclidJustin Clarke-Doane in Ethics (via the NYT):

It is commonly suggested that evolutionary considerations generate an epistemological challenge for moral realism. At first approximation, the challenge for the moral realist is to explain our having many true moral beliefs, given that those beliefs are the products of evolutionary forces that would be indifferent to the moral truth. An important question surrounding this challenge is the extent to which it generalizes. In particular, it is of interest whether the Evolutionary Challenge for moral realism is equally a challenge for mathematical realism. It is widely thought not to be. For example, Richard Joyce, one of the most prominent advocates of the Evolutionary Challenge, goes so far as to write, “the dialectic within which I am working here assumes that if an argument that moral beliefs are unjustified or false would by the same logic show that believing that 1 + 1 = 2 is unjustified or false, this would count as a reductio ad absurdum.”1 He assures the reader, “There is … evidence that the distinct genealogy of [mathematical] beliefs can be pushed right back into evolutionary history. Would the fact that we have such a genealogical explanation of … ‘1 + 1 = 2’ serve to demonstrate that we are unjustified in holding it? Surely not, for we have no grasp of how this belief might have enhanced reproductive fitness independent of assuming its truth.”2 Similarly, Walter Sinnott-Armstrong writes, “The evolutionary explanations [of our having the moral beliefs that we have] work even if there are no moral facts at all. The same point could not be made about mathematical beliefs. People evolved to believe that 2 + 3 = 5, because they would not have survived if they had believed that 2 + 3 = 4, but the reason why they would not have survived then is that it is true that 2 + 3 = 5.”3 Finally, Roger Crisp writes, “In the case of mathematics, what is central is the contrast between practices or beliefs which develop because that is the way things are, and those that do not. The calculating rules developed as they did because [they] reflect mathematical truth. The functions of … morality, however, are to be understood in terms of well-being, and there seems no reason to think that had human nature involved, say, different motivations then different practices would not have emerged.”4

In this article, I argue that such sentiments are mistaken. I argue that the Evolutionary Challenge for moral realism is equally a challenge for mathematical realism.