Formally, I classify myself as a gnostic atheist, meaning I know there are no gods. Most atheists (from what I read online) appear to be agnostic atheists, people who are without gods but who do not claim to know there are no gods. Some people who fit this description simply call themselves agnostic. But, on formal forums, like reddit’s atheism subreddit, all who are without gods are atheists and agnostic or gnostic is a statement of whether they know or have doubt. Similarly, they allow for agnostic theists, those who believe in god(s) but have some doubt.
In no other area of discussion do we expect certainty or proof when we speak of knowledge. Nearly all knowledge, outside of mathematics, is empirical knowledge, gained by empirical evidence.
Empirical evidence, also known as sensory experience, is the knowledge received by means of the senses, particularly by observation and experimentation. The term comes from the Greek word for experience, ἐμπειρία (empeiría).
After Immanuel Kant, in philosophy, it is common to call the knowledge gained a posteriori knowledge (in contrast to a priori knowledge).
This is the type of knowledge we use when we say that we know that if we drop a ball on the surface of the earth, it will fall. I don’t hear a whole lot of people telling me, you can’t claim to know that because you can’t prove it. But, indeed we cannot. We know the ball will fall because it has done so the last gazillion times we performed the experiment.
For some reason, most people expect that if you say that you know there are no gods, that this one case of knowledge requires certainty. We do not require certainty from any other type of knowledge. Why do we demand certainty to state knowledge only when we are discussing knowledge of the existence or non-existence of gods?
Why this one?
Nowhere in the definition of knowledge does it ever specify that we must have 100% certainty.
So, when I say I know there are no gods, I mean it the same way that I know the ball will drop or that I know the planet on which we live will continue to rotate through the night causing the appearance of a sunrise in the morning, even if it is blocked by clouds. Night will become day as the earth rotates. I know it. You know it. We cannot prove it to 100% certainty. We only know that it has always done so before.
To begin our discussion, we have to classify gods. This way we can address different claims of gods individually.