Often I see atheists say they do not have an active belief in the nonexistence of God, only a lack of belief in God.
I see where they are coming from, but I have a suspicion that they're equivalent.
I'd imagine they would not be equivalent under the circumstances that one does not have a concept of X. So it can be said they lack belief in the existence of X. But, if one does have a concept of X, then there seems to be three options: belief in the existence of X, belief in the nonexistence of X, or undecided.
For example, an isolated tribe of people can be said to lack belief in the existence of a toaster because they have no concept of a toaster. But, the moment you explain the concept of a toaster to them, they can either believe in the existence of a toaster, believe in the nonexistence of a toaster, or be undecided on the matter.
Or would the undecided option be "lacking belief"?