Definition:Universal Quantifier

Definition
The symbol $\forall$ is called the universal quantifier.

It expresses the fact that, in a particular universe of discourse, all objects have a particular property.

That is:
 * $\forall x:$

means:
 * For all objects $x$, it is true that ...

In the language of set theory, this can be formally defined:
 * $\forall x \in S: P \left({x}\right) := \left\{{x \in S: P \left({x}\right)}\right\} = S$

where $S$ is some set and $P \left({x}\right)$ is a propositional function on $S$.

Propositional Expansion
The universal quantifier can be considered as a repeated conjunction:

Suppose our universe of discourse consists of the objects $\mathbf X_1, \mathbf X_2, \mathbf X_3, \ldots$ and so on.

Variants
Some authors use $\left({x}\right)$ to mean $\forall x$, but the bespoke symbol is usually preferred as there is then no room for ambiguity.

Some authors use $\wedge$ or $\bigwedge$, which is appropriate when considering the propositional expansion.

Historical Note
The symbol $\forall$ was first used by in.

He invented it in analogy with the existential quantifier symbol $\exists$ which he borrowed from.

himself used the notation $\left({x}\right)$ for for all $x$. See his.

Also see

 * Definition:Universal Statement


 * Definition:Existential Quantifier
 * Definition:Existential Statement