Since last time I came across a reasonable explanation of Atheism vs. Agnosticism based on the roots of the words. Theism vs. Atheism is a question of what you believe, Gnosticism vs. Agnosticism is a question of what you claim to know.

Theist: I believe there is a god

Atheist: I do not believe there is a god (does not imply active disbelief, just a lack of belief)

Gnostic: I know for sure that my belief is true (somehow)

Agnostic: I do not know for sure that my belief is true.

So either Gnostic position (Theist or Atheist) would be to some degree faith based, but in practice you’ll find that most hard atheists are taking that position on the basis of lack of evidence – in the same way as we all say we ‘know’ that there are no unicorns, the hard atheist says he ‘knows’ there is no god.

Then you’re into the question of what it means to ‘know’ something – what standard is required for something to be called knowledge, how we ascertain what is true, and that’s a can of worms and a half. Take the strictest possible view of knowledge and you’ve got Cartesian doubt, which unless you follow Descartes twisted logic (I don’t) leaves you with no knowledge beyond your own mind (possibly not even that). There are other standards of knowledge, a “justified, true belief” being one. Doesn’t help much, just shifts the question onto whether or not it’s true, which is what we were questioning in the first place.