Hold on lil sis. I want to nail your epistemology down.
You said that "An atheist is a person that doesn't accept theistic propositions as being true. This will depend on what theistic propositions are" is the definition of atheism with the addition of "that will depend on what theistic propositions are".
Is it your subjective definition of the term Atheism or is it the normal definition of atheism that the world at large uses?
This is my definition, but it is echoed by some atheists defining similar things in different terms. For instance, George H. Smith uses the term "weak atheist" to mean essentially the same thing. I try to be more descriptive to avoid potential problems in definitions.
1. If its your subjective definition, then all your definitions are subjective, and that's your methodology. If its the common definition I would like to see who makes that kind of definition. Which people argue, by name or/and group, and what is the argument?
The common arguments over the definition are thus: some people say that atheism is "the belief that there are no gods." Some people say that's too strong, and atheism is just "the lack of belief that there are gods." For instance some people call the first example "strong atheism" and the second example "weak atheism." Then, George H. Smith and some others make a distinction between explicit atheism (chosen atheism, atheism that is consciously decided on after being exposed to beliefs about gods) and implicit atheism (non-chosen atheism, atheism that might exist because, say, someone was born on an island and has never heard of the concept of gods hypothetically; or children too young to have been taught about gods, etc.)
There are more battles over this word than even that, and that is why I hate it and don't use it; and that is why I just define it as succinctly as I can to be perfectly clear what I mean when I say it.
2. You said "theistic propositions". What are theistic propositions? What does that mean?
A theistic proposition is a proposition formed on the foundation that theism is true; that a god or gods exist. "God flooded the Earth" is a theistic proposition, "God exists" is a theistic proposition, "Mars helped the Romans win wars" is a theistic proposition.
Please let me know if that needs further clarification or anything.
When I say I'm an atheist, I mean to say that if I evaluate all of the propositions that I believe are true, I don't find any of them to be theistic.