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laws of thought

 
Britannica Concise Encyclopedia: laws of thought
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Traditionally, the three fundamental laws of logic: (1) the law of contradiction, (2) the law of excluded middle (or third), and (3) the principle of identity. That is, (1) for all propositions p, it is impossible for both p and not p to be true (symbolically, ¬(p Ù ¬p)); (2) either p or not p must be true, there being no third or middle true proposition between them (symbolically p Ú ¬p); and (3) if a propositional function F is true of an individual variable x, then F is true of x (symbolically, (x) [F(x) É F(x)]). Another formulation of the principle of identity asserts that a thing is identical with itself, or (x) (x = x).

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Philosophy Dictionary: laws of thought
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Logic is badly described as investigating the laws of thought. Logic seeks to discover how thoughts, in the sense of the combination of propositions held at one time, must be structured, if they are to conform to the demands of consistency. It does not deal with the diachronic processes whereby one thought succeeds another. The laws of thought in this sense are not known and neither is it known that there should be any such laws, not because the mind is a sphere of chaos, but because mental descriptions may not be apt for embedding in laws. See anomalous monism.

 
 

 

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Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Philosophy Dictionary. The Oxford Dictionary of Philosophy. Copyright © 1994, 1996, 2005 by Oxford University Press. All rights reserved.  Read more