It is hard to answer your question without knowing your context. I'll assume you have had a formal logic course which usually teaches the deductive syllogism.

It is hard to answer your question without knowing your context. I'll assume you have had a formal logic course which usually teaches the deductive syllogism. For example; P1: All men are mortal. P2: Socrates is a man. Ergo: Socrates is mortal. So this is one of the standard forms of a deductive syllogism (there are many others). The basic idea is that if you accept that premises 1 & 2 are true then the inference must follow otherwise your thinking includes a contradiction. E.g. All men are mortal, Socrates is a man, but if you think that Socrates is immortal then it implies a contradiction so one or both of your premises are wrong or your belief that Socrates is immortal is wrong. In formal logic courses in college they swamp you with all the variants of the deductive syllogism and what gets lost is that they are all based on Aristotle's Law of Identity. The Law of Identity basically says "A is A", a thing that exists is what it is and that contradictions cannot exist. So if you find a contradiction in your thinking then you have gone off the rails somewhere in that process. So Popper's falsifiability principle is implicitly based on deductive logic which in turn is based on Aristotle's Law of Identity. Popper's mistake was ignoring induction or generalization which is evident even in the syllogism above. The premise "All men are mortal" is a generalization not a deductive conclusion; where do these premises come from? So deduction (and falsifiability) is dependent on induction which his theory completely ignores so it is DOA.