 The idea that a rule of inference cannot be introduced as a premise in an inference in accordance with it, on pains of an infinite regress, was also reprised by Ryle (Ryle 1971, vol. II, 216 &amp; 238). But he used it to argue for his celebrated distinction between ‘knowing how’ and ‘knowing that’: ‘‘Knowing a rule of inference is not possessing a bit of extra information. Knowing a rule is knowing how. It is realised in performances which conform to the rule, not in theoretical citations of it.’’ (Ryle 1971, vol. II, 217). However, if ‘knowing how’ is no longer a state of mind (even dispositionally), then the view is no longer Cook Wilson’s.