Glossary Of Philosophic Terms
In Support of blupete's Essay "On Philosophy"
-D- [TOC]
Deductive Reasoning:
§ I quote Professor Morris Kline of New York University:
"However basic the concepts and axioms, it is the deductions from the axioms that allow us to acquire totally new knowledge to correct our sense perceptions. Of the many types of reasoning - for example, inductive, analogical, and deductive - only deductive guarantees the correctness of the conclusion. To conclude that all apples are red because 1000 apples are found to be red is inductive reasoning, therefore not reliable. Similarly, the argument that John should be able to graduate from college because his identical twin who inherited the same faculties did so, is reasoning by analogy, and is certainly not reliable. Deductive reasoning, on the other hand, although it can take many forms, does guarantee the conclusion. Thus, if one grants that all men are mortal and Socrates is a man, one must accept that Socrates is mortal. The principle of logic involved here is one form of what Aristotle called syllogistic reasoning. Among other laws of deductive reasoning Aristotle included the law of contradiction (a proposition cannot be both true and false) and the law of excluded middle (a proposition must be either true or false).
"He and the world at large accepted unquestioningly that these deductive principles which applied to any premises yielded conclusions as reliable as the premises. Hence, if the premises were truths, so would be the conclusions. It is worthy of note that Aristotle abstracted the principles of deductive logic from the reasoning already practiced by mathematicians. Deductive logic is, in effect, the child of mathematics." [Mathematics and the Search for Knowledge (Oxford University Press, 1985) p. 48.]
(See further under Inductive Thinking.)
