Logic: (objective) regulating principles of reality, meaning and truth; (subjective) the systematic study of systems of natural language or artificial notations.

The study of arguments and things essential to their appraisal as good or bad.

The normative study of good reasoning.There are as many types of logic, as there are types of reasoning, but logic is most closely associated with inference and argument. Inference means the drawing of a conclusion from evidence (premises). Historically it had been widely believed that there are just two types of inference: deductive and inductive; and so traditionally logic was thought to divide into deductive and inductive logic. But in the late 20th century it became clear that that “inductive” and “deductive” do not exhaust the types of inferential connection. Prominent alternatives (well ensconced in the literature) are conductive inference (Govier, 1987), defeasible inference (Pollock, 1995) and nonmonotonic reasoning. In some circles, “inductive logic” is defined as any type of non-deductive logic, thus preserving the dualism of the two types of logic as deductive and inductive. However, so construed induction covers a wide variety of different modes of reasoning, from probabilistic reasoning to balance of considerations (where no quantification is attempted) and no common denominator is apparent.

Govier, T. (1987). Essays in Argument Analysis and Evaluation.Dordrecht: Foris [Essays that cover topics in informal logic, argument analysis and critical thinking by one of Canada’s leading philosophers and argumentation theorists.]

(Pollock, 1995). See Defeasible Reasoning.

Source: What is Good? What is Bad? The Value of All Values across Time, Place and Theories’ by John McMurtry, Philosophy and World Problems, Volume I-III, UNESCO in partnership with Encyclopedia of Life Support Systems: Oxford, 2004-11.