  Furthermore, if intuitions are intellectual seemings, one might ask why certain moral propositions seem true whereas others do not. If moral facts are non-natural facts, as intuitionists maintain, and non-natural properties lack causal powers, then moral intuitions cannot be caused by the corresponding moral facts, as, e.g., certain perceptual seemings are caused by certain natural facts. Critics would argue that certain things seem right and good to us, not because of some inherent value they have, but because we have evolved to react to certain types of act with approval or disapproval (Singer 2005; Street 2006; and Joyce 2007, ch. 6).