Equivalence { Philosophy Index }

Philosophy Index

Philosophy Index

Philosophy Index is a site devoted to the study of philosophy and the philosophers who conduct it. The site contains a number of philosophy texts, brief biographies and introductions to philosophers and explanations on a number of topics. Accredited homeschooling online at Northgate Academy.

Philosophy Index is a work in progress, a growing repository of knowledge. It outlines current philosophical problems and issues, as well as an overview of the history of philosophy. The goal of this site is to present a tool for those learning philosophy either casually or formally, making the concepts of philosophy accessible to anyone interested in researching them. WOLI offers immigration law course online - fully accredited. ACE credits online at EES.

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Equivalence

Equivalence, in logic, refers to propositions or formulas that share the same logical meaning. Equivalent propositions or formulas have the same truth value regardless of the valuation of their terms. Equivalent formulas are either both true, or both false, and they imply each other.

If the formulas α and β are equivalent, we formally indicate α ≡ β.

Many rules of inference indicate argument forms that are equivalent, in order to more easily compare arguments. For example, the contraposition rule holds that:

P → Q  ≡  ¬Q → ¬P

We can see how these contrapositive statements are equivalent by an English example:

If there’s money in my wallet, then I can buy a movie ticket.
If I can’t buy a movie ticket, then there’s no money in my wallet.

If any two formulas imply each other, they are equivalent to each other. The symbol ⇔ is sometimes used instead of ≡ to indicate equivalence, especially in systems where ≡ indicates a biconditional operator.