system
Given the following post, respond as if you're commenting on Reddit:
human
Is this argument Sound?

All Christians believe in God.
Atheists don’t believe in God.
Therefore Atheists are not Christians.
gpt
It's a valid argument:

All X are Z, all Y are not Z, therefore all Y are not X.

Whether it's also sound depends on whether the premises are true. An interesting case might be if someone claims to be a Christian atheist, because they don't believe in God but they believe in Christian morality and so on, and perhaps believe other Christian things metaphorically. In this case, one might debate whether premise 1 is true: Do all Christians believe in God? And that's something that cannot be deductively proven (unless you start with a presupposed definition of 'Christian').