Formal logic is the study of inference conducted with purely formal content, where the validity of an argument depends solely on its logical form rather than on the meaning of its terms. At its core, logic is concerned with arguments, which are sets of statements (called premises) offered as reasons to support another statement (called the conclusion). When evaluating arguments, two central concepts apply: an argument is valid when, if all its premises are true, the conclusion must necessarily be true, and it is sound when it is both valid and has all true premises. Soundness is the only condition that guarantees a true conclusion.
A key distinction in logic is between deductive and inductive reasoning. Deductive reasoning moves from general premises to a specific conclusion that follows with certainty, so that given true premises the conclusion cannot be false. In contrast, inductive reasoning moves from specific observations to a general conclusion that is merely probable. A classic deductive example runs: all mammals are warm-blooded, dogs are mammals, therefore dogs are warm-blooded. An inductive counterpart would be: every swan I have observed is white, therefore all swans are probably white. Because of this difference, deductive arguments are judged valid or invalid in an all-or-nothing sense, while inductive arguments are judged strong or weak depending on how probable their conclusion is given the premises.