So as the definitions show, atheism IS a theory or belief system (or doctrine as used above).
As your quoted assertion contends in Message ID: 434227: "... as the definitions show, atheism IS a theory or belief system ..." and I replied that atheism is not a "belief SYSTEM". It involves disbelieving any religionist claims that 'god exists' and the burden of proof is on those that claim a positive assertion, (rather than upon the logical fallacy of requiring proof of a negative assertion).
Given your demonstrated lack of comprehension in these matters, your claimed GPA is dubious.
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I have no reason to lie about a GPA online? And I merely answered your assertion that I did not excel in school with a factual respresentation that I do, in fact, do just that.
The reason that your claimed GPA was brought up, (initially by you, I'll add), was that it seemed dubious that such a grade point average could be supported by a demonstrably low reading comprehension level. As an aside, your assertion does not constitute a "factual representation";
only a scanned and unaltered copy of your school transcripts would. This won't be necessary as it was only one example of differentiating a 'fact' from a 'claim'.
So you are saying atheism involes only disbelief not belief?
"Atheism is, in a broad sense, the rejection of belief in the existence of deities. In a narrower sense, atheism is specifically the position that there are no deities. Most inclusively, atheism is simply the absence of belief that any deities exist. Although some atheists have adopted secular philosophies, there is no one ideology or set of behaviors to which all atheists adhere. In practical or pragmatic atheism, also known as apatheism, individuals live as if there are no gods and explain natural phenomena without resorting to the divine. The existence of gods is not rejected, but may be designated unnecessary or useless; gods neither provide purpose to life, nor influence everyday life, according to this view. A form of practical atheism with implications for the scientific community is methodological naturalism—the "tacit adoption or assumption of philosophical naturalism within scientific method with or without fully accepting or believing it." "-- wikipedia
The answer to your question then is that atheism is subdivided into "positive atheism, negative atheism, pragmatic atheism, axiological atheism and theoretical atheism. So no, atheism does not "only" involve disbelief. Note the excerpt "... there is no one ideology or set of behaviors to which all atheists adhere."
Doesn't atheism rely on a belief in science explaining all matters of the world either now or sometime in the future? Or would you not agree with that?
No, I don't agree with that interpretation since "belief" isn't necessary in the context of the scientific method. Either such methods can, (or will), produce cause and effect explanations of various phenomenon, (and so far, they've done a pretty good job with non-metaphysical stuff), or they cannot. Applying physical scientific methodology to largely nonphysical 'metaphysics' gets into a gray area where the two are hypothesized to overlap. Theoretical physics, for instance, is often an outrider into those overlapping realms.