A type of quantifier $\text{Q}x$ such that a sentence $\text{Q}x\phi \left(x\right)$ is true if and only if the class of objects satisfying the formula $\phi \left(x\right)$ is of a particular cardinality or among a particular class of cardinalities. For example, the Keisler quantifier $\text{Q}x$ named for the mathematician H. Jerome Keisler (1936– ) is interpreted as ‘there exist uncountably many $x$s…’ so that $\text{Q}x\phi \left(x\right)$ is true in a model when there are at least ${\omega }_1$ many elements satisfying $\phi \left(x\right)$.