Theism is the belief in a god or gods or the supernatural. Atheism is the lack of belief in a god or gods or the supernatural.
Defining god. Before I can define atheism I need to define what I see as 3 types of gods.
- The cultural god/s as represented by one of the 4000+ religions
- Impersonal detached god (Deism)
- First cause, intelligent creator of the universe
All 3 definitions of god share the “creator of the universe” attribute.
Atheists don’t believe in any of these types of gods. However, as agnostics, we acknowledge the (small) possibility that any of them could exist. But as atheists our lives are governed by probability rather than possibility.
Unlike the major religions, atheism has no foot print. It has no direct evidence because it is the lack of belief / belief that something does not exist. So rather than prove atheism is true, we prove that theism is not true and therefore atheism is true.
In defending atheism there is no silver bullet argument that disproves all of the religions or proves atheism. There are arguments for and against each of the religions and for and against atheism. Rather you have to look at the totality of evidence and make a judgement call.
But even then we are subject to confirmation bias as our prior beliefs are generally more influential than the actual evidence.