There are undoubted pleasures to be had from being a pedant. It can be satisfying to point out someone's faulty grasp of the subjunctive, or to tick them off for splitting an infinitive. The pleasure comes not so much from the fact of drawing attention to another's error—which the pedant sees as a regrettable by-product of his duties—as from the feeling of complete rightness that it brings. For the pedant, armed with the weapons of etymology and grammar, is pretty much unanswerable. And in life, the sensation of being unanswerably right is rare.
Yet pedants make the mistake of not knowing when the "errors" they point out matter, and when they don't. For them, such distinctions are immaterial; all that matters are the rules. But language is about usefulness, not rules; the rules serve usefulness, not the other way around. Let's take that pedant's favourite—"decimate." Literally, "decimate" means reduce by one tenth (it derives from the Roman army's disciplinary practice of killing one man in ten). But nowadays it is often used to mean "vanquished." Does this matter? Now that Roman legions no longer roam the earth, the word decimate, meant in its true sense, is pretty useless. So to insist on correct usage is, in effect, to kill it off. Another bugbear of pedants is using "the" before "hoi polloi" (in Greek, "hoi" means "the"). But again, as most people don't know what "hoi" means, who really cares?
There are of course some common misuses that do matter: "disinterested" vs "uninterested"; "coruscating" vs "excoriating." But a lot of the time, the berations of pedants can be safely ignored. Or, if they chastise you for ending a sentence with a preposition, you can respond by saying: "That is the sort of pedantry up with which I shall not put."
