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It depends on what knowledge they have. If they are on the same level, then probably nobody would win. Plus, usually "a win" is not a purpose in this kind of debates, but rather sharing your believes and more learn about other religions, faiths.
A discussion between an atheist, an agnostic and a theist should not be characterized as a battle. There would be no "winner" since the issue is one of belief for certain of the participants and not based on any proof or even a preponderance of evidence. They could discuss and share their various beliefs and philosophies but there could be no bond fide "winner". The problem lies in characterizing each position as an adversarial one. The question fails to acknowledge all the thousands of different systems of belief that have evolved along with humankind. None is the winner and yet they are all winners according to those people who have adopted them. However, when people think of differences as a battle there could be no winner unless someone resorts to the violence which we have seen throughout history waged by people of one religion against another.
He is a theist - he describes himself as a Muslim.
She is catholic.
I presume you mean, Richard Branson. He is an atheist.
Richard Dreyfuss has described himself as a believer in God, but does not affiliate with any specific religion. This would classify him as a theist.
Atheist - If he is sure there there is no specific god because of the impossibility and/or improbability of his existence. Agnostic - Not sure whether there is a god or not. Usually does not care. An atheist is the opposite of a theist. The theist believes there is evidence for the existence of their favorite god. The atheist does not. It would be illogical for the atheist to "deny" the existence of something for which there is no evidence. Atheism is merely the lack of a belief. Knowledge is absolute. Since nobody can know with absolute certainty no gods exist, everyone is agnostic. So the so-called "agnostic" has the same lack of knowledge as the atheist or theist has. It's just commonly accepted that an agnostic does not commit either way.
These are fine distinctions, but some philosophers define a range of beliefs: Thiest - certain that god exists. Weak thiest - acknowledges that one can't be certain, but believes. Agnostic - neither believes nor disbelieves. Weak atheist - acknowledges that one can't be certain, but disbelieves. Strong atheist - certain there is no god. As you can see, "weak atheists" hold the middle ground - in fact, most atheists are probably weak atheists - they acknowledge that certainty isn't possible, but it is very unlikely that god actually exists.
He an anti-theist (against religion) but more-so agnostic when it comes to the existence of a so called "God".
Just ask them if they are atheist, theist or agnostic. most won't be ashamed to tell you. However if they don't agree with your simple 3 category breakdown you might get an answer like None of those, Secularist, pagan, Rastafarian, Epicurean, Stoic, Freethinker, etc. You will then have to shuffle your categories.
The opposite form of atheist is theist.
That is the correct spelling of "gnostic" (capitalized Gnostic referring to the belief).The similar word is the adjective or noun agnostic(neither a theist nor atheist).
No. An atheist (no god or without god) is sure that they don't believe in gods. However not being sure has a name as well, it is most often called agnostic (not knowing) behavior. From "not being sure" you may progress through studying the question and discussing the issue to being either an atheist, agnostic or theist. A fourth option, non-theist, best describes groups like Buddhists who don't feel the issue of whether there is a god or not is worthwhile pursuing.
Why would it vary between theist and atheist? Obviously, there's no much point asking how church is going.