A person who believes that the human mind cannot know whether there is a God or an ultimate cause, or anything beyond material phenomena. Thus, because he believes that a human being cannot know whether God exists, an agnostic must believe that he does not know whether God exists. However, a person that believes he does not know whether God exists is not necessary agnostic. An agnostic cannot say whether they positively believe God exists or that they positively believe that God does not exist.

The term is derived from the 'unknown' God in Acts 17:23, and was first used in 1869, by Thomas Henry Huxley. The word is from a-, "without" + gnostic, which is from the Greek gnostikos (γνωστικος), which is from gnosis, "knowledge." In a letter dated March 13, 1881, Richard Holt Hutton wrote that the term 'agnostic' was "suggested by Prof. Huxley at a party held previous to the formation of the now defunct Metaphysical Society, at Mr. James Knowles's house on Clapham Common, one evening in 1869, in my hearing. He took it from St. Paul's mention of the altar to 'the Unknown God.'"

See: agnosticism
See also: atheism, theism