| Transformation rules |
|---|
| Propositional calculus |
|
Rules of inference Rules of replacement Commutativity Distributivity Double negation De Morgan's laws Transposition Material implication Exportation Tautology |
| Predicate logic |
| Universal generalization Universal instantiation Existential generalization Existential instantiation |
A rule of inference is a rule justifying a logical step from hypothesis to conclusion. There are several rules of inference which utilize the existential quantifier.
Existential introduction (∃I) concludes that, if the propositional function is known to be true for a particular element of the domain of discourse, then it must be true that there exists an element for which the proposition function is true. Symbolically,
The reasoning behind existential elimination (∃E) is as follows: If it is given that there exists an element for which the proposition function is true, and if a conclusion can be reached by giving that element an arbitrary name, that conclusion is necessarily true, as long as it does not contain the name. Symbolically, for an arbitrary c and for a proposition Q in which c does not appear:
must be true for all values of c over the same domain X; else, the logic does not follow: If c is not arbitrary, and is instead a specific element of the domain of discourse, then stating P(c) might unjustifiably give more information about that object.
Read more about this topic: Existential Quantification, Properties
Other articles related to "rules of inference":
... For example, if it's true that I'm breathing if and only if I'm alive, then it's true that if I'm breathing, I'm alive likewise, it's true that if I'm alive, I'm breathing ... Formally ( A ↔ B ) ∴ ( A → B ) also ( A ↔ B ) ∴ ( B → A ) ...
Famous quotes containing the words rules of, inference and/or rules:
“... geometry became a symbol for human relations, except that it was better, because in geometry things never go bad. If certain things occur, if certain lines meet, an angle is born. You cannot fail. It’s not going to fail; it is eternal. I found in rules of mathematics a peace and a trust that I could not place in human beings. This sublimation was total and remained total. Thus, I’m able to avoid or manipulate or process pain.”
—Louise Bourgeois (b. 1911)
“Rules and particular inferences alike are justified by being brought into agreement with each other. A rule is amended if it yields an inference we are unwilling to accept; an inference is rejected if it violates a rule we are unwilling to amend. The process of justification is the delicate one of making mutual adjustments between rules and accepted inferences; and in the agreement achieved lies the only justification needed for either.”
—Nelson Goodman (b. 1906)
“Serious sport has nothing to do with fair play. It is bound up with hatred, jealousy, boastfulness, disregard of all rules and sadistic pleasure in witnessing violence: in other words it is war minus the shooting.
”
—George Orwell (1903–1950)