Posterior Analytics (Bouchier)/Book I/Chapter XVIII

Chapter XVIII: On ignorance as resulting from defective sense perception

 * Ignorance is the result of a defect in sense. Universals can only be attained by the help of Induction. Induction however depends on Sensation, the objects of which are particulars, of which no science is possible. Consequently Induction is necessary for the conversion of Sensation into Scientific knowledge.

It is also clear that if some branch of our perceptive faculties prove deficient the corresponding branch of science, which cannot be attained without those faculties, must fail also; that is to say if it be agreed that we must acquire knowledge either through induction or demonstration. Now although demonstration proceeds from universals and induction from particulars, it is impossible to attain to the knowledge of universals except by means of induction. Even the matter of the abstract sciences may be established through induction, since some qualities belong peculiarly to each class of thing and make them what they are, even though these qualities are not really separable from the things themselves. Induction without the power of perception is impossible, for perception is concerned with particulars, which cannot be grasped at all by means of science. The reason of this is that we cannot attain to universals without induction, nor use induction without sense perception.