The purpose of this post is just to define terms used in my series on evidential arguments for naturalism.
Before discussing specific arguments for and against atheism, I think it would be useful to define some terms. In doing so I will adopt the definitions put forth by Professor Theodore M. Drange in his excellent essay, “Atheism, Agnosticism, Noncognitivism.” Consider the sentence, “God exists.” Do you think that sentence is meaningful? In other words, do you think that sentence is either true or false? If you think the sentence, “God exists” is a bunch of meaningless nonsense, you are a noncognitivist with respect to God-talk. (However, I don’t recommend using that word at cocktail parties!) If you do think the sentence is meaningful, then ask yourself a follow-up question: is that sentence true or false? If you think that sentence is true or probably true you are a theist. If you think that sentence is false or probably false you are an atheist. Finally, if you do not have a position on whether the sentence is true or false then you are an agnostic.
By defining terms in the above manner, I am rejecting the definition of terms used by many atheists, where atheism is defined as simply the lack of theistic belief. I am aware that this will be controversial with some people who self-identify as an atheist; indeed, I used to passionately defend that definition of atheism on Usenet. The only problem with that definition, however, is that nobody outside of nontheistic circles ever uses it. When the average “person on the street” uses the word “atheist,” they mean someone who holds the belief that God does not exist. Thus, when nontheists use the word “atheism” in a nonstandard way, it makes communication with the general public difficult. And while it might be possible to persuade the general public to use the ‘correct’ definition of atheism, it would hardly be worth the effort. The primary dispute between theists and nontheists is whether God exists; we should focus our energy on that issue. (For further argument, please see my post, “The Definition of Atheism, the Anal-Retentive Defense of Etymological Purism, and Linguistic Relativism.”)
Metaphysical naturalism is the hypothesis that the natural world is a closed system, which means that nothing that is not a part of the natural world affects it. Metaphysical naturalism denies the existence of all supernatural beings, including gods and God, and so entails atheism.