The common use of the term “agnostic” doesn’t make any sense.
No one should be absolutely certain about anything they believe, indeed most aren’t. That’s because certainty has no bearing on something being true, and I’m not arrogant enough to say I’ve nailed something down permanently; save a few experiencial brute facts. Psychology isn’t Epistemology.
So, “agnostic” can only be said to describe the fact that “I’m not absolutely certain”, in which case that word attaches to all my beliefs and as such, describes nothing at all. Saying “I believe” is no different than saying “Though I’m not certain, I believe …”. Even in conversation, we only do that sort of thing when we feel we are certain: “I’m positive that …”, or, “Surely!”, or, “I’m one hundred percent certain that …”. Otherwise, we simply say “I think this is the case”.
Agnosticism is instead the position that nothing can be known about transcendent realities.
An Agnostic Theist is then one who believes there may be or is a God, but admits that he doesn’t and can’t know anything about God.
An Agnostic Atheist would be one who rejects all god-talk as false when asserted, for the fact that such talk has no referent but admits he can’t know if they are otherwise actually true.
An Ignostic is an Agnostic who doesn’t even take the question of transcendent realities seriously for the fact that god-talk can’t have a referent and is then literal nonsense.
A.J. Ayer’s “Language, Truth, And Logic” does a great job of scolding everyone but Ignostics and being forgiving of the position theists are in, though he thinks Theism is bunk too. He outlines the strengths and weaknesses of all. A great read for anyone curious about the logic behind these various sorts of ideas about the existence of the divine.