Mr Kahn has examined the probable quantitative result of such factors as these in certain hypothetical special cases. But, clearly, it is not possible to carry any generalisation very far.
" They're extremely rational and they're much better in some ways at doing inferential learning" – using patchy information to make accurate generalisations about a messy world – " than any other creature that we know of."
There are broadly three possible answers: (1) that it is itself known a priori; (2) that it is a postulate; (3) that it is an empirical generalisation from past instances in which it has been found to hold.