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Full Idea
For no very good reason, three principles have been singled out by tradition under the name of 'Laws of Thought': the laws of identity ('what is, is'), contradiction ('never be and not be'), and excluded middle ('always be or not be').
Gist of Idea
Three Laws of Thought: identity, contradiction, and excluded middle
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 7)
Book Ref
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.40
A Reaction
'For no very good reason' seems a bit unfair, probably to medieval logicians, who deserve more respect. Russell suggests that the concept of implication deserves to be on the list. Presumably optimism about thinking is a presupposition of thought.
| 19360 | General principles, even if unconscious, are indispensable for thinking [Leibniz] |
| 19404 | Necessities rest on contradiction, and contingencies on sufficient reason [Leibniz] |
| 7807 | The laws of thought are true, but they are not the axioms of logic [Bolzano, by George/Van Evra] |
| 6933 | The laws of reality are also the laws of thought [Feuerbach] |
| 8939 | We should not describe human laws of thought, but how to correctly track truth [Frege, by Fisher] |
| 5396 | Three Laws of Thought: identity, contradiction, and excluded middle [Russell] |
| 5405 | The law of contradiction is not a 'law of thought', but a belief about things [Russell] |
| 9131 | Two long understandable sentences can have an unintelligible conjunction [Sorensen] |
| 6560 | The law of noncontradiction is traditionally the most basic principle of rationality [Fogelin] |