I have written many times on the meaning of agnosticism, but I haven't focused much on why it was coined or its purpose. I think getting into the purpose of agnosticism would help people better understand it. To most people, agnosticism is just a position of uncertainty that also challenges those that claim to know God exists and those that claim no God exists. This is in line with the current dictionaries and at least one of Thomas Huxley's statements on his agnosticism,
"Some twenty years ago, or thereabouts, I invented the word "Agnostic" to denote people who, like myself, confess themselves to be hopelessly ignorant concerning a variety of matters, about which metaphysicians and theologians, both orthodox and heterodox, dogmatise with the utmost confidence;" (1)

However, if we look at some of Huxley's other statements, instead of just one in isolation, we find that what he really was against was 'dogmatism'. For those not familiar with the term, dogmatism involves treating beliefs as if they were true, and oftentimes in a close-minded way. The Church would oftentimes treat their religious beliefs that way, and some atheists would also treat their philosophical beliefs that way. Dogmatism boils down to being unwarranted certainty. In response to this, Huxley advocated for principles that would counteract dogmatism, such as being open-minded, freethinking, non-partisan, etc (hence, the themes of this forum).

So in short, the goal of agnosticism was to be a position against dogmatism or unwarranted certainty (as opposed to being uncertain about everything). When dogmatic individuals or groups tend to be close-minded and regard their views as unquestionable, Huxley counters that with being open-minded. Where dogmatic people elevate their beliefs and ideologies, Huxley counters that with freethinking or with only being certain towards views that are backed by logic and science. Where dogmatist try to rely on authority, power, or some established orthodoxy, Huxley counteracts that by being non-partisan (this is more implied though going by his actions to steer away from labels or "ists" of all kinds).

1. Huxley, Thomas. Agnosticism: A Symposium. The Agnostic Annual, (1884).

Further reading:
1. Read Possibilities and Impossibilities by Huxley. This is his best expression of open-mindedness where he explains why he's open to anything that is logically possible, as opposed to only things that are physically possible (i.e. materialism).
2. Full list of Huxley's writings, go here.
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