 Physicalism is the view that our mathematical sentences and theories are about ordinary physical objects. John Stuart Mill (1843) developed a view of this kind. On his view, mathematics is just a very general natural science. Thus, for instance, according to Mill, the sentence ‘2 + 3 = 5’ is not a claim about abstract objects (the numbers 2, 3, and 5); rather, it’s a claim about piles of physical objects (in particular, it tells us that if we push a pile of two objects together with a pile of three objects, we’ll get a pile of five objects. (Phillip Kitcher (1984) and the early Penelope Maddy (1990) have also endorsed views with “physicalistic leanings”, but in the end, neither is plausibly interpreted as falling into this camp. Maddy’s early view is better thought of as a non-traditional sort of platonism, because according to this view, mathematics is about nonphysical objects that exist in space and time; and Kitcher’s view is best thought of as a kind of paraphrase nominalism, because on his view, mathematical utterances turn out not to be about any actually existing objects.)