Semantics began its life in the late 19th century as a technical word in the field of semiotics, referring to such topics as the relation between signs and the things to which they refer. It was quickly adopted by the field of linguistics, and applied to the study of the meaning of words. When it is encountered in general use today (among non-specialists) the word is often seen in the phrase just arguing semantics, which appears to indicate that the speaker intends for semantics to signify something unimportant and trivial, or unrelated to the discussion.
This expression will occasionally puzzle people who understand that semantics has something to do with meaning, on the grounds that the meaning of words is of some importance in a discussion or argument. How has semantics come to be used to refer to two things that are fairly disparate in character: either meaning itself or unimportant things? It would appear to have gained this extended meaning over several decades, beginning in the middle of the 20th century.
An early example of the broadened sense, used in a sneering fashion by Lewis Gannett, can be found in The New York Herald Tribune on June 15th, 1945:
There seems to be some argument about whether Mauldin’s cartoons are Art. Such argument is mere semantics.
Another article in the same paper, this one from 1956, shows semantics again being employed in a somewhat dismissive fashion, as the governor of the state of New York, W. Averell Harriman, used the word as he campaigned for the Democratic nomination for the presidency:
Asked on his arrival about this apparent modification of his views, Gov. Harriman said he would not get into arguments over “word semantics.”
By the early 1960s arguing semantics has taken on a somewhat more refined meaning, referring more to a form of linguistic nit-picking than it did to a concerted attempt to decipher the true meaning of a word. Andrew Berding, in his 1962 book Foreign Affairs and You!, wrote “…the representative of the various departments spend too much time and mental energy arguing semantics and unimportant detail.”
By the early 1960s we see the full phrase, just arguing semantics, being used to indicate that one is quibbling about something irrelevant or unknowable. It can be found in a transcript from a senate hearing from 1963, with testimony before the Committee on Armed Services:
Mr. Fee: So you have essentially proven something like two-thirds of your total problem, leaving one-third with some state of it unknown. Is this a fair statement?
Dr. Bradbury: I am afraid we are just arguing semantics with the word “prove.”
Does this shift in usage indicate that semantics is now approaching a state of being a contronym (a word having two meanings that contradict one another)? Possibly, although it does not have quite the same degree of difference that such words often have, for instance cleave, which can mean both ‘to cut apart’ and ‘to stick together’. The phrase arguing semantics doesn’t really indicate that the discussion is about something other than meaning, just that the precise nature of that meaning is not terribly important.
That's something to keep in mind if you find yourself in an argument with a linguist or a semiotician.