I have often said that there are three kinds of Atheism; namely, strong Atheism, which entails commitment to the proposition “God does not exist” being true (or alternatively a commitment to the proposition “God exists” being false), Positivism, which is the position that the phrase “God exists” is not a proposition, and Agnosticism which is the position that, though the sentence “God exists” is meaningful (such that it could be true, or false) its truth value is either in principle inscrutable or else just hasn’t yet been determined to the agnostic’s satisfaction. Sometimes it is said that agnostics simply lack a belief that God exists, and they are not committed to the proposition that “God does not exist.”
However, clearly there is a difference between somebody who apprehends that “God exists” is meaningful, and who simply isn’t yet ready to assign it a truth-value either way, and somebody who simply strictly lacks a belief in God’s existence. Rocks, trees, cats, dogs and babes all lack a belief that God exists, but we wouldn’t want to call them Agnostics, because an Agnostic is one who apprehends that the phrase “God exists” is meaningful, but isn’t as of yet ready to assign it a truth-value. A Babe (Baby) is not an agnostic, whether weak or strong (weak being the kind who has said that they themselves haven’t determined whether God exists or not, and strong being an agnostic who believes that nobody else can determine the truth-value of the proposition “God exists” either). So, perhaps we should say that some things/persons qualify as Atheists simply because they lack any beliefs at all. We can imagine that Babies, along with perhaps the mentally handicapped, would by default be ‘Atheists’.
Alternatively, maybe we ought just to exclude those things/persons which lack any beliefs at all as candidates for Atheism/Theism. That would bring Atheism back down to three kinds rather than four.