I've used agnostic as my yardstick since college....and I think Thomas Huxley explains it well:
"Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle ... Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable.
[15][16][17]"
— Thomas Henry Huxley
https://en.wikipedia.org/wiki/Agnosticism
"Being a scientist, above all else,
Huxley presented agnosticism as a form of demarcation. A hypothesis with no supporting objective, testable evidence is not an objective, scientific claim. As such, there would be no way to test said hypotheses, leaving the results inconclusive. His agnosticism was not compatible with forming a belief as to the truth, or falsehood, of the claim at hand.
Karl Popper would also describe himself as an agnostic.
[18] According to philosopher
William L. Rowe, in this strict sense, agnosticism is the view that human reason is incapable of providing sufficient rational grounds to justify either the belief that God exists or the belief that God does not exist.
[2]"
I've a lot of sympathy with Agnosticism. Many new atheists refer to themselves as agnostic-atheists precisely to emphasise their acceptance that proving God's non-existence is impossible, and I can understand that. But, realistically, some things that can't be proven to be unreal are so astoundingly unlikely that to say one wouldn't rule it out just because it can't be proven is stretching an intellectual exercise pretty far. I could, as many atheists do, claim to be a
de facto atheist, who doesn't rule out the existence of God but considers it so unlikely that in every practical sense I live my life assuming He doesn't exist. That's fine, but really, I'd be lying if I said I thought there was even a remote chance that this particular piece of mythology was true.
Many atheists claim atheism isn't a belief because they don't believe in God's non-existence, they just don't belive in his existence. This is a useful way of batting away the frequent claim from theists that atheism is just another belief, as though all beliefs have equal likelihood, and it also makes atheists feel sanctimoniously rational and scientific, which they seem to get a buzz from. They frequently differentiate between a 'belief' and atheism by saying that a person doesn't change a belief according to new evidence, it remains fixed, while atheists, being such rational beings, would accept the possibility of God if corroborating evidence emerged.
This makes intuitive sense, but I don't think it's actually true in real life. I don't think people really believe things in that way. Some people might think their faith is unshakeable. Many of the most vocal on-line atheists who now claim a belief is something that doesn't change ironically also talk of their own past with religion, when they cried for the unbelievers among their families and friends who were destined for Hell if they didn't listen to sense and embrace their saviour. They were sure of their faith and that nothing would shake it, yet they now celebrate their atheism. People do change their beliefs, and they do so because of evidence, or because they're no longer getting whatever emotional benefits they once enjoyed from those beliefs. Some people will ignore or explain away evidence which is contrary to their beliefs, cognitive bias being a curse we all bear as humans, and others will tweak their beliefs to incorporate new evidence. But if something is utterly ridiculous, as the God hypothesis is, there is no shame in saying 'I believe God isn't real,' just as there is no shame in saying, 'I believe there are no microscopic kangaroos fighting gun toting panda bears for dominance of hummus deposits beneath the surface of Mars.' If a shining angelic being appears before the world and proclaims God's existence, I would certainly accept the possibility that he's being truthful, and will no longer be able to talk of believing God isn't real. That won't happen, though, because God isn't real.
Incidentally, the above argument about the nature of belief and that atheism is a belief is either utterly wrong or I frequently fail to present it coherently. I don't bother any more, but on various atheist website I used to have constant discussions with other atheists about this, but they remained adamant that a belief is unchangeable and that atheism wasn't one. There were fallings out over this. Sometimes, there was simply no response to the argument at all. I suspect that many new atheists haven't really delved too deep into this particular piece of atheist dogma and are just parroting the words of their comrades because on social media they will still confidently respond to the accusation that atheism is just another belief with something like, 'Atheism is a
lack of belief. Look it up!' I've looked it up. Some dictionaries refer to it clearly as a belief, some as a lack of belief, and some give both options. Perhaps atheists need to tell their critics in which dictionary they are to use when looking up the word.
Anyone who reads this whole post gets a gold star.