This is from Nanavira's notes on Dhamma, Phassa footnote e:
The notion of sensation, however, as we see from the dictionary's definition, is an abomination from the start—how can one 'perceive the state of one's senses' when it is precisely by means of one's senses that one perceives? (See MANO.)
Another individual's perception (with his eye) of the state of my eye may well have, in certain respects, a one-one correspondence with my perception (with my eye) of, say, a tree (or, for that matter, a ghost, or, since the eye as visual organ extends into the brain, a migraine); but it is mere lazy thinking to presume from this that when I perceive a tree I am really perceiving the state of my eye—and then, to account for my sensation, inferring the existence of a tree in a supposed 'external' world beyond my experience. The reader is referred to Sartre's excellent discussion of this equivocal concept (op. cit., pp. 372-8), of 8which we can give here only the peroration. 'La sensation, notion hybride entre le subjectif et l'objectif, conçue à partir de l'objet, et appliquée ensuite au sujet, existence bâtarde dont on ne saurait dire si elle est de fait ou de droit, la sensation est une pure rêverie de psychologue, il faut la rejeter délibérément de toute théorie sérieuse sur les rapports de la conscience et du monde.' ('Sensation, hybrid notion between the subjective and the objective, conceived starting from the object, and then applied to the subject, bastard entity of which one cannot say whether it is de facto or de jure,—sensation is a pure psychologist's day-dream: it must be deliberately rejected from every serious theory on the relations of consciousness [which, for Sartre, is subjectivity] and the world.')
Descartes, it seems, with his 'representative ideas', is the modern philosopher primarily responsible for the present tangle—see Heidegger, op. cit., p. 200 et seq. (Heidegger quotes Kant as saying that it is 'a scandal of philosophy and of human reason in general' that there is still no cogent proof for the 'being-there of things outside us' that will do away with all scepticism. Then he remarks 'The "scandal of philosophy" is not that this proof is yet to be given, but that such proofs are expected and attempted again and again'.) [Quote edited for formatting.]
Firstly what are these 'represenative ideas' that he is talking about?
Why are Descartes' representative ideas the cause of the contradictory notion of sensation?