What is Epistemology?:
Empiricism: knowledge is obtained through experience.
Rationalism: knowledge can be acquired through the use of reason.
Why is Epistemology Important?:
Why Does Epistemology Matter to Atheism?:
Epistemology, Truth, and Why We Believe What We Believe:
Questions Asked in Epistemology:
How can we know it?
Why do we know some things, but not others?
How do we acquire knowledge?
Is knowledge possible?
Can knowledge be certain?
How can we differentiate truth from falsehood?
Why do we believe certain claims and not others?
Important Texts on Epistemology:
Treatise on Human Nature, by David Hume
Critique of Pure Reason, by Immanuel Kant
An Essay Concerning Human Understanding, by John Locke
What’s the Difference Between Empiricism and Rationalism?:
Empiricism and rationalism exhaust all possibilities — either knowledge can only be acquired after experience or it is possible to acquire at least some knowledge before experience. There are no third options here (except, perhaps, for the skeptical position that no knowledge is possible at all), so everyone is either a rationalist or an empiricist when it comes to their theory of knowledge.
Atheists tend to be either exclusively or primarily empiricists: they insist that truth-claims be accompanied by clear and convincing evidence which can be studied and tested. Theists tend to be much more wiling to accept rationalism, believing that "truth" can be attained through revelations, mysticism, faith, etc. This is consistent with how atheists tend to place primacy on the existence of matter and argue that the universe is material in nature whereas theists tend to place primacy on the existence of mind (specifically: the mind of God) and argue that existence is more basically spiritual and supernatural in nature.
Rationalism is not a uniform position. Some rationalists will simply argue that some truths about reality can be discovered through pure reason and thought (examples include truths of mathematics, geometry and sometimes morality) while other truths do require experience. Other rationalists will go further and argue that all truths about reality must in some way be acquired through reason, normally because our sense organs are unable to directly experience outside reality at all.
Empiricism, on the other hand, is more uniform in the sense that it denies that any form of rationalism is true or possible. Empiricists may disagree on just how we acquire knowledge through experience and in what sense our experiences give us access to outside reality; nevertheless, they all agree that knowledge about reality requires experience and interaction with reality.