 To highlight the general difficulties with Cartesianism is only part of Ryle’s destructive strategy. The other part is to show how logical absurdities arise with one particular offshoot of the Official Doctrine: one he dubs “the intellectualist legend”. This involves the type-error or category mistake of supposing that what distinguishes certain performances from others that are perceptually similar (in one sense of ‘perceptual’) is the addition of some non-perceptual feature. The Official Doctrine construes this feature as a special mental  accompaniment.[7]  The intellectualist legend, accepting this construal of the Official Doctrine, says that intelligent or rational behaviour can be accommodated or explained by some sort of theoretical operations involving these hidden accompaniments. But if this is a mistake, it is a big one; for it is made not only throughout various sub-branches of philosophy but also in collaborating disciplines. (The idea, for example, that intelligence involves physically realised, (non-introspectible) theoretical (computational) operations is one of the founding blocks of the cognitive sciences.)