Kitap 4
28
And in general, if only the sensible exists, without animate things there would be nothing; for there would be no sense-faculty.
29
That there would be neither sensible qualities nor sensations is probably trueCf. Aristot. De Anima 425b 25-426b 8.(for these depend upon an effect produced in the percipient), but that the substrates which cause the sensation should not exist even apart from the sensation is impossible.
30
For sensation is not of itself, but there is something else too besides the sensation, which must be prior to the sensation; because that which moves is by nature prior to that which is moved, and this is no less true if the terms are correlative.
1
But there are some, both of those who really hold these convictions and of those who merely profess these views, who raise a difficulty; they inquire who is to judge of the healthy man, and in general who is to judge rightly in each particular case. But such questions are like wondering whether we are at any given moment asleep or awake;
2
and all problems of this kind amount to the same thing. These people demand a reason for everything. They want a starting-point, and want to grasp it by demonstration; while it is obvious from their actions that they have no conviction. But their case is just what we have stated beforeAristot. Met. 4.4.2.; for they require a reason for things which have no reason, since the starting-point of a demonstration is not a matter of demonstration.
