Agnosticism is the philosophical view that the truth
values of certain claims—particularly theological claims regarding the existence
of God, gods, or deities—are unknown, inherently unknowable, or incoherent, and
therefore, (some agnostics may go as far to say) irrelevant to life. The term
and the related agnostic were coined by Thomas Henry Huxley in 1869, and are
also used to describe those who are unconvinced or noncommittal about the
existence of deities as well as other matters of religion. The word agnostic
comes from the Greek a (without) and gnosis (knowledge). Agnosticism, focusing
on what can be known, is an epistemological position (dealing with the nature
and limits of human knowledge); while atheism and theism are ontological
positions (a branch of metaphysics that deals with what types of entities
exist). Agnosticism is not to be confused with a view specifically opposing the
doctrine of gnosis and Gnosticism—these are religious concepts that are not
generally related to agnosticism.
Agnosticism is distinct from strong atheism (also called positive atheism or dogmatic atheism), which denies the existence of any deities. However, the more general variety of atheism, weak atheism (also called negative atheism, and sometimes neutral atheism), professes only a lack of belief in a god or gods, which is not equivalent to but is compatible with agnosticism. Critical atheism admits that a god or gods are meaningful concepts but the evidence for them is not in hand, so a default position of not believing in them must be taken in the interim.
Agnostics may claim that it isn't possible to have absolute or certain spiritual knowledge or, alternatively, that while certainty may be possible, they personally have no such knowledge. In both cases, agnosticism involves some form of skepticism towards religious statements. This is different from the simple irreligion of those who give no thought to the subject.
Agnosticism has suffered more than most expressions of philosophical position from terminological vagaries. Data collection services ,  often display the common use of the term, distinct from strong atheism in its lack of disputing the existence of deities. Agnostics are listed alongside secular, non-religious, or other such categories.
Other variations include:
Among the most famous agnostics (in the original sense) have been Robert G. Ingersoll, Thomas Henry Huxley, Charles Darwin, and Bertrand Russell. Some have argued from the works of David Hume, especially Dialogues Concerning Natural Religion, that he was an agnostic, but this remains subject to debate.
Agnostic views are as old as philosophical skepticism, but the terms agnostic and agnosticism were created by Huxley to sum up his thoughts on contemporary developments of metaphysics about the "unconditioned" (Hamilton) and the "unknowable" (Herbert Spencer). It is important, therefore, to discover Huxley's own views on the matter. Though Huxley began to use the term "agnostic" in 1869, his opinions had taken shape some time before that date. In a letter of September 23, 1860, to Charles Kingsley, Huxley discussed his views extensively:
And again, to the same correspondent, May 6, 1863:
Of the origin of the name agnostic to describe this attitude, Huxley gave (Coll. Ess. v. pp. 237-239) the following account:
Huxley's agnosticism is believed to be a natural consequence of the intellectual and philosophical conditions of the 1860s, when clerical intolerance was trying to suppress scientific discoveries which appeared to clash with a literal reading of the Book of Genesis and other established Jewish and "Christian" doctrines. Agnosticism should not, however, be confused with natural theology, deism, pantheism, or other science positive forms of theism.
By way of clarification, Huxley states, "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" (Huxley, Agnosticism, 1889). While A. W. Momerie has noted that this is nothing but a definition of honesty, Huxley's usual definition goes beyond mere honesty to insist that these metaphysical issues are fundamentally unknowable.
Bertrand Russell's pamphlet, Why I Am Not a "Christian", based on a speech delivered in 1927 and later included in a book of the same title, is considered a classic statement of agnosticism. The essay briefly lays out Russell’s objections to some of the arguments for the existence of God before discussing his moral objections to "Christian" teachings. He then calls upon his readers to "stand on their own two feet and look fair and square at the world," with a "fearless attitude and a free intelligence."
In 1939, Russell gave a lecture on The existence and nature of God, in which he characterised himself as an agnostic. He said:
However, later in the same lecture, discussing modern non-anthropomorphic concepts of God, Russell states:
In Russell's 1947 pamphlet, Am I An Atheist Or An Agnostic? (subtitled A Plea For Tolerance In The Face Of New Dogmas), he ruminates on the problem of what to call himself:
In his 1953 essay, What Is An Agnostic? Russell states:
However, later in the essay, Russell says:
Note that he didn't say "supreme" or "supernatural" intelligence, as these terms are metaphysically loaded.
For Russell, then, agnosticism doesn't necessarily assert that it is in principle impossible to know whether or not there is a God. Moreover, "An Agnostic may think the "Christian" God as improbable as the Olympians; in that case, he is, for practical purposes, at one with the atheists."
Logical positivists, such as Rudolph Carnap and A. J. Ayer, are sometimes thought to be agnostic. Using arguments reminiscent of Wittgenstein’s famous "Whereof one cannot speak, thereof one must be silent," they viewed any talk of gods as literally nonsense. For the logical positivists and adherents of similar schools of thought, statements about religious or other transcendent experiences could not have a truth value and were deemed to be without meaning. But this includes all utterances about God, even those agnostic statements that deny knowledge of God is possible. In Language, Truth and Logic Ayer explicitly rejects agnosticism on the grounds that an agnostic, despite claiming that knowledge of God is not possible, nevertheless holds that statements about God have meaning. This position, however, is valid only in the case of agnostics who define their agnosticism in this fashion. Ignostics define agnosticism in a manner consistent with the logical positivist view, holding theism to be incoherent.