Considering the instability of nonlinear dynamics,the deductive inference rule Modus ponens itself is not enough to guarantee the validity of reasoning sequences in the real physical world,and similar results cannot necessarily be obtained from similar causes.Some kind of stability hypothesis should be added in order to draw meaningful conclusions.Hence,the uncertainty of deductive inference appears to be like that of inductive inference,and the asymmetry between deduction and induction becomes unrecognizable such as to undermine the basis for the fundamental cleavage between analytic truth and synthetic truth,as W.V.O.Quine pointed out.Induction is not inferior to deduction from a pragmatic point of view.