There’s a lovely piece in the Chronicle of Higher Education by the linguist Geoffrey Pullum, on the strange phrase “‘Twas ever thus”. It survives in the language as an idiom, even though the grammar used in it is completely archaic. You can’t, as Pullum points out, use “ever” in affirmative clauses: we’d normally say “always” or (in different contexts) “sometimes”. (“I don’t ever eat mustard” is fine, but “I ever eat mustard” is bizarre.)
Also, the Pullum piece has cheered me up immensely by informing me that there is a character in Charles Dickens’s The Old Curiosity Shop called “Dick Swiveller“, which sounds like a highly specific job title in a Californian porn studio (“Assistant Dick Swiveller: Suzi Banghard”), or the sort of hilarious homophobic abuse a drunken fratboy might yell at someone who isn’t very good at sports.
Anyway. I quite like these “‘Twas ever thus”-style little linguistic fossils. One I was thinking about a few months ago is “Come hell or high water“: “I’ll save you, come hell or high water!” This use of “come” to mean, roughly, “even if I am faced with”, is completely archaic: it would never be used in any non-idiomatic way (“We’ll go to the park, come rain or shine” is OK, because it’s an idiom; “I’ll get there on time, come bad traffic or planned engineering works on the Hammersmith and City line” sounds weird and affected). “As it were” is another. And there’s a good piece on archaic words that have only survived in idioms (“kith”, “dint”, “umbrage”, “shrift”) here. They’re like the oxbow lakes of language, or the vestigial organs: as language changes it leaves these little traces of its evolution, preserved, to switch metaphors for a moment, in amber.
I started writing this thinking I might have a point to make, but it turns out I don’t at all. Plus ça change, and all that.
Update: I’ve changed it from “frozen in amber” to “preserved in amber”, because that’s more correct, and I’ve changed the Assistant Dick Swiveller’s name from “Mitzi Suxx” to “Suzi Banghard”, because I thought that was funnier.