Q: What is the difference between “it’s all relative” and “it’s all academic”? It seem to me that there’s something hypothetical about both of them.
A: The two usages, which showed up in the early 1800s, have a sense of uncertainty about them. “Relative” here means indefinite or indeterminate, while “academic” means impractical, theoretical, or inconsequential.
The Oxford English Dictionary defines “to be relative” as “to be evaluated differently depending on a person’s perspective; to be incapable of definitive or absolute evaluation. Frequently in it’s all relative.”
In other words, it’s all in the eye of the beholder, a usage that showed up in the early 1600s.
The earliest example for “it’s all relative” in the OED is from an 1804 case report by Christopher Robinson, a judge on the High Court of Admiralty:
“It may be difficult to lay down the precise bounds, where ordinary commerce ends, and extraordinary speculation begins. It is all relative.”
The dictionary defines “academic” in the sense you’re asking about as “not leading to a decision; unpractical; strictly theoretical or formal. Now also in weakened sense: of no consequence, irrelevant.”
The dictionary’s first example is from an 1812 issue of the Monthly Review, a British literary journal:
“His erudition must be worked into the edifice, not exhibited in lumpish disconnection. He must preserve the epic form, without sliding into academic discussion.”
The OED doesn’t have a citation for “it’s all academic.” But examples aren’t hard to find.
The earliest example we’ve found is from the February 1892 issue of Books, a publication of the Denver (CO) Public Library: “It is all academic to the last degree. It is perhaps the airiest of suspicions.”
In a recent example, Richard Posner, who had just retired as a federal judge in Chicago, said in a Sept. 14, 2017, interview that he was ordinarily polite in court but found it irritating when lawyers were unprepared or talkative or went off the point:
“So I do get annoyed; I’m criticized for that. I should control myself, but of course now, it’s all academic. I’m not a judge. Too late to correct me.”
As for the etymology, “academic” is ultimately derived from the classical Latin acadēmicus, describing the ancient Academy of Athens or its philosophy, while “relative” ultimately comes from the classical Latin relātus, past participle of referre (to refer).