In predicate logic, an existential quantification is the predication of a property or relation to at least one member of the domain. It is denoted by the logical operator symbol ∃ (pronounced "there exists" or "for some"), which is called the existential quantifier. Existential quantification is distinct from universal quantification ("for all"), which asserts that the property or relation holds for any members of the domain.

Symbols are encoded U+2203 ∃ there exists (HTML: ∃ ∃ as a mathematical symbol) and U+2204 ∄ there does not exist (HTML: ∄).

Consider a formula that states that some natural number multiplied by itself is 25.

0·0 = 25, or 1·1 = 25, or 2·2 = 25, or 3·3 = 25, and so on.

This would seem to be a logical disjunction because of the repeated use of "or". However, the "and so on" makes this impossible to integrate and to interpret as a disjunction in formal logic. Instead, the statement could be rephrased more formally as

For some natural number n, n·n = 25.

This is a single statement using existential quantification.

Paul Watson (born December 2, 1950) is a Canadian animal rights and environmental activist, who founded and is president of the Sea Shepherd Conservation Society, a direct action group devoted to marine conservation.

The Toronto native joined a Sierra Club protest against nuclear testing in 1969. He was an early and influential member of Greenpeace, crewed and skippered for it, and later was a board member. Watson argued for a strategy of direct action that conflicted with the Greenpeace interpretation of nonviolence, was ousted from the board in 1977, and subsequently left the organization. That same year, he formed Sea Shepherd Conservation Society. The group is the subject of a reality show, Whale Wars.

He also promotes veganism, voluntary human population control, and a biocentric, rather than anthropocentric, worldview.

Paul Watson was born in Toronto to Anthony Joseph Watson and Annamarie Larsen, and grew up in St. Andrews, New Brunswick. After working as a tour guide at Expo 67, the World's Fair that took place in Montreal in 1967, Watson "rode the rails" in boxcars west to Vancouver.