logic

Logic (from ancient Greek λόγος (logos), originally meaning the word, or what is spoken, but coming to mean thought or reason) is the study of arguments. Its primary task is to set up systems and criteria for distinguishing good from bad arguments. Arguments express inferences — the processes whereby new assertions are produced from already established ones. As such, of particular concern in logic is the structure of arguments — the formal relations between the newly produced assertions and the previously established ones, where "formal" means that the relations are independent of the assertions themselves. Just as important is the investigation of validity of inference, including various possible definitions of validity and practical conditions for its determination. It is thus seen that logic plays an important role in epistemology in that it provides a mechanism for extension of knowledge.

As a byproduct, logic provides prescriptions for reasoning, that is, how people – as well as other intelligent beings, machines, and systems – ought to reason. Such prescriptions are not essential to logic itself, however; rather, they are an application. How people actually reason is usually studied in other fields, including cognitive psychology.

Traditionally, logic is studied as a branch of philosophy. Since the mid-1800s logic has been commonly studied in mathematics, and, even more recently, in computer science. As a science, logic investigates and classifies the structure of statements and arguments and devises schemata by which these are codified. The scope of logic can therefore be very large, including reasoning about probability and causality. Also studied in logic are the structure of fallacious arguments and paradoxes. The ancient Greeks divided dialectic into logic and rhetoric. Rhetoric, concerned with persuasive arguments, would currently be seen as contrasted with logic, in some sense, as is dialectic in most of its acquired meanings.