Agnosticism is the view that the truth value of certain claims—especially claims about the existence or non-existence of any deity, but also other religious and metaphysical claims—is unknown or unknowable. Agnosticism can be defined in various ways, and is sometimes used to indicate doubt or a skeptical approach to questions. In some senses, agnosticism is a stance about the difference between belief and knowledge, rather than about any specific claim or belief. In the popular sense, an agnostic is someone who neither believes nor disbelieves there is a God, whereas an atheist disbelieves there is a God. In the strict sense, however, agnosticism is the view that human reason is incapable of providing sufficient rational grounds to justify knowledge whether God exists or does not. Within agnosticism there are agnostic atheists (who do not believe any deity exists, but do not deny it as a possibility) and agnostic theists (who believe a God exists but do not claim to know that).
Thomas Henry Huxley, an English biologist, coined the word agnostic in 1869. However, earlier thinkers and written works have promoted agnostic points of view. They include Protagoras, a 5th-century BCE Greek philosopher, and the Nasadiya Sukta creation myth in the Rig Veda, an ancient Sanskrit text. Since Huxley coined the term, many other thinkers have written extensively about agnosticism.