A proposition (1) is said to be true because it has not been disproved or (2) is said to be untrue because it has not been proved. What is not disproved on a given occasion is not necessarily true. Is a scientific theory accepted as true because you cannot disprove it? Rather, the theory must be verified positively. Every person who presents a proposition in argument has the obligation to offer at least one reason in defense of it. Likewise, your opponent's successful attack on all premises or reasons you advance does not in all strictness make his position right and yours wrong. All he has shown is that your position is not true for your reasons. Other people, now or later, may be able to produce better reasons. Similarly, your being able to show that your adversary in his defense has involved himself in contradiction is not sufficient to prove him wrong. Smith may be arguing that the taking of life is evil, but admits that he doesn't object to killing animals for food. There is contradiction and confusion, but Smith may still be right that the taking of life is evil.