出典:Wikipedia
出典:『Wikipedia』 (2011/08/02 14:28 UTC 版)
In logic, the law of excluded middle (also known as the principle of excluded middle or excluded middle or excluded third) is the principle that for any proposition, either that proposition is true, or its negation is. The principle can be expressed in either a logical or a semantical form. The semantical form uses the non-logical word "true", as above. The logical form uses only logical expressions "either", "or" and can be expressed by the formula "P ∨ ¬P": "either P or not P", where "P" is schematic for any proposition such as 'snow is white', 'Socrates is running' and so on.