  Induction is the inverse process of deduction, but it is a much more complicated mode of reasoning. Induction proceeds according to certain rules of thumb, trial and error, and past attempts.  Induction of simple identities becomes very complex as soon as more than just a few terms are involved. Induction of partial identities starts from a certain premise in disjunctive form A = B ·|· C ·|· D ·|· … ·|· P ·|· Q, and then we need propositions that ascribe a certain property to all individuals: B = BX, C = CX, …, Q = QX. Substituting and rearranging yield the desired result A = AX. According to Jevons this is the most important scientific procedure, as “a great mass of scientific truths consists of propositions of this form A = AB”. Jevons recognises the problem of induction — that we can never be sure to predict the future based on past knowledge. Jevons needs to bring in principles of number and theory of probability to deal with this matter.