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The three modes of logical inference are deduction, induction and abduction. At this point it may be may be helpful to look at formal definitions of the terms.

Deduction

Wikipedia defines deductive reasoning as:

... reasoning in which the conclusion is necessitated by, or reached from, previously known facts. If the premises are true, the conclusion must be true. This is distinguished from abductive and inductive reasoning, where the premises may predict a high probability of the conclusion, but do not ensure that the conclusion is true.

Induction

The Wikipedia defines inductive reasoning as:

... the process of reasoning in which the premises of an argument are believed to support the conclusion but do not ensure it. It is used to ascribe properties or relations to types based on tokens (i.e., on one or a small number of observations or experiences); or to formulate laws based on limited observations of recurring phenomenal patterns.

Abduction

The Wikipedia defines abductive reasoning as:

... the process of reasoning to the best explanations. In other words, it is the reasoning process that starts from a set of facts and derives their most likely explanations. The term abduction is sometimes used to mean just the generation of hypotheses to explain observations or conclusions, but the former definition is more common both in philosophy and computing.

Developing a Working Set of Tools

The assertions of these two modes of forms of inference may or may not be 'true' according to the circumstances - certainly, they can never be 'true' with the absolute metaphysical certainty characteristic of logical deduction. The meaning of 'inferring from consequences' is discussed in the following sections.

Note that the definitions presented below are overly broad and might even be considered eccentric from the exacting perspective of classical and modern mathematical logic. The intention is not to probe the deep inner workings of mathematical logic but to develop a set of workable set of tools to solve common problems. The definitions given below might legitimately be said to represent a 'hammer and tongs' approach to using logical inference in rule based systems ( when it works at all ).