An agnostic holds that it is impossible to know for certain whether God or gods exist, while an atheist simply does not believe any gods exist. One is a position on what can be known; the other is a position on what is believed. Someone can describe themselves as agnostic rather than atheist to mark that difference.
The core difference
Agnostic is a position on whether God's existence can be known at all, while atheist is a position of not believing gods exist.
- agnostic — believing it is impossible to know for certain whether God or gods exist: She describes herself as agnostic rather than atheist.
- atheist — a person who does not believe that any gods or deities exist: She has identified as an atheist since college.
How to tell them apart
A simple hook: agnostic is about knowledge (‘I don't know’), atheist is about belief (‘I don't believe’). The word agnostic was coined in 1870 by Thomas Henry Huxley from Greek roots meaning ‘not known,’ to describe someone who neither affirms nor denies God's existence. Atheist, by contrast, comes from Greek atheos, ‘godless’ — a direct statement of non-belief.
The mix-up comes up because the two are not strictly opposites; a person can be both agnostic and atheist at once, uncertain that God's existence can be proven yet still not believing in one. Where the words clearly split is in emphasis: agnostic leaves the question open, atheist answers it.
