Atheism Defintion

For a significant portion of history, the standard definition of atheism was specifically the positive assertion that "God does not exist".

While many modern atheists define the term as a simple "lack of belief" (a psychological state), this is a relatively recent shift in the word's primary usage.

Here is the breakdown of how the definition has evolved from "denial" to "lack of belief."

1. The Historical Definition (16th–Mid-20th Century)

From its entry into the English language (via the French athéisme) in the 16th century until the mid-20th century, atheism was almost exclusively defined as the specific metaphysical claim that there is no God.

Academic Standard: In philosophy, atheism was traditionally viewed as the mirror opposite of theism. If theism was the proposition "God exists," atheism was the proposition "God does not exist."

The Agnostic Distinction: Because "atheist" was seen as a claim of knowledge (asserting a negative), it was distinct from "agnostic." In the late 19th century, Thomas Henry Huxley coined the term agnosticism specifically to describe people who "lacked belief" but refused to assert that God didn't exist because they felt the evidence was insufficient to claim either way.

2. The Shift: Antony Flew & The "Presumption of Atheism"

The definitions began to change significantly in 1976, when the philosopher Antony Flew wrote The Presumption of Atheism.

Flew argued that the burden of proof should lie with the believer. To achieve this logically, he proposed re-defining "atheism" not as a positive claim ("God does not exist") but as a negative state ("I do not hold a belief in God"). He explicitly admitted he was using the word in a new, "unusual" way to win a debate advantage. 

He wrote: "The word 'atheism', however, has in this contention to be construed unusually... I want the word to be understood not positively but negatively." This "negative definition" became incredibly popular among secular activists because it removed the burden of proof. If you are just "lacking belief," you don't have to prove anything, since this is just a statement about one's inner psychological state.

Note: Flew later rejected atheism ("there is no God" definition) and wrote There Is a God: How the World's Most Notorious Atheist Changed His Mind

Update:

"That was done to win a debate advantage", was not a quote, but that idea was in his book "The Presumption of Atheism" - 3rd chapter, 2nd paragraph. Here it is in full:

The word 'atheism', however, has in this contention to be construed unusually. Whereas nowadays the usual meaning of 'atheist' in English is 'someone who asserts that there is no such being as God', I want the word to be understood not positively but negatively. I want the originally Greek prefix 'a' to be read in the same way in 'atheist' as it customarily is read in such other Greco-English words as 'amoral', 'atypical', and "asymmetrical'. In this interpretation an atheist becomes: not someone who positively asserts the non-existence of God; but someone who is simply not a theist. Let us, for future ready reference, introduce the labels 'positive atheist' for the former and 'negative atheist' for the latter. What the protagonist of my presumption of atheism wants to show is that the debate about the existence of God ought to be conducted in a particular way, and that the issue should be seen in a certain perspective. His thesis about the onus of proof involves that it is up to the theist: first, to introduce and to defend his proposed concept of God; and, second, to provide sufficient reason for believing that this concept of his does in fact have an application. Here is a PDF of Chapter 3 - The Presumption of Atheism.

The only way Flew could do this was to turn atheism from a claim into a non-claim.

3. The Current Split

Today, you will encounter two different definitions depending on who you are talking to:

• In Philosophy: Most academic encyclopedias (like the Stanford Encyclopedia of Philosophy) still define atheism as the view that there are no gods. They typically use the term "non-theism" for the broader lack of belief.

• In Public Discourse: Most self-described atheists and activist groups (like American Atheists) use the broader definition: "A lack of belief in gods."

To bridge this gap, people now often use qualifiers:

• Negative/Weak Atheism: Lacking belief (closer to the modern definition).

• Positive/Strong Atheism: Asserting God does not exist (the historical definition).

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