Logic is the study of the methods of evaluating arguments. An argument is a set of propositions consisting of one or more premises and a conclusion. The premises claim to provide reasons in support of the conclusion. Arguments are different from mere narration of facts and explanations. Propositions are typically expressed by declarative sentences. There are two types of arguments deductive and inductive. A deductive argument claims to provide conclusive support for its conclusion. An inductive argument claims to provide partial support for its conclusion; it cites evidence which makes the conclusion somewhat reasonable to believe Deductive arguments are either valid or invalid. A valid argument has the essential feature that it is impossible for its conclusion to be false while its premises are true. An argument is invalid if and only if it is not valid. An argument is deductively sound if and only if it is valid and has all true premises. An unsound argument is one which is either invalid or has at least one false premise. Since logic is a systematic study of methods and principles of correct reasoning and it teaches us the technique of testing the correctness of arguments, it can be viewed both as a science and an art. There are three fundamental laws of logic. These are (1) the law of identity, (2) the law of contradiction, and (3) the law of excluded middle. These are basic principles of correct thinking which are presupposed in any logical thinking.