Conjunction elimination

Transformation rules
Propositional calculus
Rules of inference
Implication introduction / elimination (modus ponens) Biconditional introduction / elimination Conjunction introduction / elimination Disjunction introduction / elimination Disjunctive / hypothetical syllogism Constructive / destructive dilemma Absorption / modus tollens / modus ponendo tollens
Rules of replacement
Associativity Commutativity Distributivity Double negation De Morgan's laws Transposition Material implication Exportation Tautology Negation introduction
Predicate logic
Universal generalization / instantiation Existential generalization / instantiation

In propositional logic, conjunction elimination (also called and elimination, ∧ elimination, or simplification) is a valid immediate inference, argument form and rule of inference which makes the inference that, if the conjunction A and B is true, then A is true, and B is true. The rule makes it possible to shorten longer proofs by deriving one of the conjuncts of a conjunction on a line by itself.

An example in English:

It's raining and it's pouring.

Therefore it's raining.

The rule consists of two separate sub-rules, which can be expressed in formal language as:

${\frac {P\land Q}{\therefore P}}$

and

${\frac {P\land Q}{\therefore Q}}$

The two sub-rules together mean that, whenever an instance of "$P\land Q$" appears on a line of a proof, either "$P$" or "$Q$" can be placed on a subsequent line by itself. The above example in English is an application of the first sub-rule.

Formal notation

The conjunction elimination sub-rules may be written in sequent notation:

$(P\land Q)\vdash P$

and

$(P\land Q)\vdash Q$

where $\vdash$ is a metalogical symbol meaning that $P$ is a syntactic consequence of $P\land Q$ and $Q$ is also a syntactic consequence of $P\land Q$ in logical system;

and expressed as truth-functional tautologies or theorems of propositional logic:

$(P\land Q)\to P$

and

$(P\land Q)\to Q$

where $P$ and $Q$ are propositions expressed in some formal system.