Where did the tradition of putting certain Latin or foreign (hell, they may all be Latin - I don’t know the Romance languages very well) in italics come from? Examples include sotto voce or par excellance. I did a quick look at the OED and didn’t find any explanation (admittedly, I didn’t look that hard).
Like the “no split infinitives” rule, this started up with Victorian-era prescriptive grammarians as a way of indicating to the reader that the phrase was from a foreign language. I think the assumption back then was that if you were new to reading (as so many people were), you might not know a common foreign expression from your elbow, so the printer should do something to help you out, you poor slob.
It is still commonly (though less commonly) used with completely foreign expressions like your example sotto voce, which average speakers and readers of English would have no expectation of knowing. Foreign expressions like “per se” or “adios” have been absorbed into English sufficiently that any time you see them italicized, you can count on it being an affectation.
Not bad, KTK, but it goes back way before the Victorian era. My facsimile edition of Descartes’ 1637 French work La Géometrie uses italics for Latin. And I’m sure I’ve seen the same usage in even earlier vernacular works. I would bet it predates the invention of printing but I sure hope nobody asks me to back that up.
And it’s not intended so much for novice readers (who didn’t form a big part of Descartes’ audience, for example) as simply a courtesy to all readers who are cheerfully skimming along in one language and aren’t expecting the next word they see to be in a different one. A nice invention on the part of the literate world, right up there with page numbers if you ask me.
And while I would guess that “adios” and “sympatico” are as anglicized as “canyon” or “arroyo” (even if we cheated on the spelling for “canyon”), or “blitzkrieg” or “flak”, I would disagree regarding per se, i.e., e.g., and a number of other phrases and abbreviations. Unless one wants to put forth an abomination such as “persay,” I would hold that those phrases remain Latin (as noir remains French) and they should continue to be italicized.
There is not a clean, logical determination for this, but that is how I would interpret current usage.