So I was thinking again today about a post of mine from a while ago, "Atheists who believe in God". The short version: a Pew religious survey found, incredibly, that 55% of agnostics and 21% of atheists say they believe in God or a "universal spirit". In my previous post I did joke that "in other news: 1 in 4 vegans eat meat" and so on, but I didn't quite spell out how preposterous this actually is.
An atheist, basically, is someone who lacks a belief in (any) God. So the very definition of an atheist is someone who does not believe. A theistic atheist, in other words, is a necessarily non-existent being; such a thing simply cannot exist in any possible universe. The same is true of, for example, a married bachelor. The definition of bachelor is "unmarried man", so a person cannot possibly be both a bachelor and married. The same goes for two-horned unicorns, three-sided squares, non-black black ravens and absolutely certain agnostics.
A person who self-identifies as atheist but also claims to believe in God, then, is either dumb, deeply confused or doesn't know what 'atheist' means. What certainly isn't true is that this person is actually both an atheist and a theist. (Well, at least not at the same time).