Logic is the process of reasoning based on specific principles. From the Greek logos meaning “word,” logic is study of the principles of reasoning--a set of premises that are examined and arranged so as to bring a conclusion. If A = B and B = C, then A = C.
Deductive logic is the method of validating a claim by means of supportive information where both the claim and the information are necessarily true. For example, people exist. All people breathe. Therefore, all people breathe.
Inductive logic is the method of drawing a conclusion from a set of supportive information, yet the conclusion has not yet been verified. For example, each night I get tired at 10 p.m. Therefore, I conclude that tonight I will be tired at 10 p.m.
See also Logical Fallacies.