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 Reference
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.