A strong atheist is defined as an atheist who positively asserts that no god or gods exist. The definition of strong atheist is sometimes confused with the definition of atheist. Whereas a strong atheist asserts that no gods exist, the definition of atheist is merely one who does not believe in the existence of any gods. The definition of atheist is broad whereas the definition of strong atheist is narrow. Strong atheist overlaps with positive atheist, explicit atheist, and critical atheist.
The label strong atheist is also sometimes defined as one who claims to know that no god or gods exists. This goes a step beyond simply believing that it is false that any gods exist because you can believe something is false without also claiming to know for sure that it is false. This definition is the one typically used to criticize strong atheists by arguing that it's impossible to know that no gods can or do exist, ergo strong atheists must be illogical, contradicting themselves, or have at least as much religious faith as theists.
Strong atheist. 'I know there is no God, with the same conviction as Jung "knows" there is one.'"
- Richard Dawkins, The God Delusion
