Book 3
1.53
In constructing his proofs he makes most use of induction, not always in the same way, but under two forms. For induction is an argument which by means of certain true premisses properly infers a truth resembling them. And there are two kinds of induction, the one proceeding by way of contradiction, the other from agreement. In the kind which proceeds by contradiction the answer given to every question will necessarily be the contrary of the respondent’s position, e.g. My father is either other than or the same as your father. If then your father is other than my father, by being other than a father he will not be a father. But if he is the same as my father, then by being the same as my father he will be my father.
