А то!: Sure! Absolutely! Like I’d say no!
It’s a rainy Friday in my part of the world, and there is nothing like a good pop quiz to get the blood flowing. So put your books down, turn off your phones, take out a pen or pencil, really turn off your phones this time, and answer this question: А то means a) or else; b) even; c) on second thought; d) yes!; e) none of the above; f) all of the above; g) I hate little Russian words.
If you chose f) all of the above – Садись, пятёрка! (Sit down! You get an ‘A.’) If you chose g) you also get пятёрка for honesty. Because there is nothing more difficult to get a handle on than all those “simple” words like как, так, да, вот, нет, то and so on, which when combined and recombined or said in various tones of voice create a fountain of new, contradictory meanings.
The combination а то is a conjunction or an exclamation with lots of nuanced meanings. But before we get to them, note that sometimes а то is not a conjunction or an expression. It’s just two words in a sentence: а (but or and) and то (this, the). Sometimes this can be translated as “the fact that”: А то, что Касьянов придал конфликту публичный характер, так это просто форма борьбы (But the fact that Kasyanov went public with the conflict was just a ploy in the battle). Or it might be translated as “what” or “which”: Важно не то, что он открыл, а то, какие у него свидетельства о квалификации и какая репутация (What’s important is not what he discovered, but what certificates of qualification and reputation he had).
Now then, the most common meaning of "а то" as a conjunction is “otherwise” or “or else.” It’s used in sentences that are structured like this: We need to do X or else Y will happen, with а то as the “or else.” Садитесь, а то упадёте (Sit down or else you’ll fall). Эти яблоки придётся снять прямо сейчас, а то они сгниют (We have to pick those apples right away or else they’ll spoil).
Weirdly, you can also say the seemingly negative “а не то” in these kinds of sentences and it means the same thing as the positive “а то.” Иногда засыпала сразу и спала всю ночь, а не то до рассвета читала романы (Sometimes I’d fall asleep right away and sleep through the night, or else I’d end up reading novels until dawn). Luckily this form seems somewhat dated now.
Sometimes you don’t need the first part of the sentence — speakers just cut to the “or else” part. You’re very likely to hear this short version in conversations with your significant other. You are, say, arguing against going to see your tone-deaf aunt perform in the local neighborhood playhouse performance of “Annie.” Or you refuse to buy a birthday gift for a cousin you don’t like who never thanks you anyway. You explain why you don’t want to do it. Your reasons are sound. Your significant other agrees… and then urges you to do it anyway with three words: А то неудобно (Or else it’ll be awkward).
А то + и might be translated as “or even.” В последнее время происходит следующее: соответствуя букве Конституции, закон искажает, а то и противоречит ее духу (In recent years the following occurs: while keeping to the letter of the Constitution, a law twists or even contradicts its intent). This might also be translated as “or sometimes even”: Но тогда почему же в большинстве цивилизованных стран принято отдавать детей в школу с шести, а то и с пяти лет? (Well then, why is it that in the majority of civilized countries children are usually sent to school at the age of six or sometimes even at age five?)
When you add on “и вовсе” to “а то,” you get a meaning like “or even completely”— a scaling up of consequences. Here’s an example when someone wants to give their beloved house pet a folk remedy: Вы можете сильно навредить своему коту, а то и вовсе его убить (You might seriously injure or even kill your cat). Here’s another example of consequences being scaled up: Некоторые трудности, испытываемые обвинением, преодолеть трудно, а то и вовсе невозможно (Some difficulties are hard, if not utterly impossible, for the prosecution to overcome).
Those are the main meanings of “а то” as a conjunction. But it can also be something of an exclamation. It can be used when a speaker declines to do something, and after refusing or dithering exclaims that he’ll do it after all. I think of this as the “on second thought” meaning: Не хочется больше... А то налейте еще стакан! (I don’t want anymore… well, on second thought, pour me another glass!)
This brings us to my favorite usage, the “hell, yes” meaning. This is a stand-alone response to a question that has an obvious answer. –Если я куплю билеты на кино с твоим любимым актёром, пойдёшь со много? –А то! (“If I buy tickets to see a movie with your favorite actor, will you go with me?” “Abso-frigging-lutely!”) This might also be the “why would you even ask” usage: –Тебе понравилось кино? –А то! (“Did you like the movie?” “What do you think?”) You can say this around the dinner table: –Можно мне добавки? –А то! (“May I have seconds?” “You bet!”)
This usage has great snark potential. When your significant other starts in on the dreadful singing aunt or the horrible ungrateful cousin, you can put on your best long-suffering smirk and say: А то я не знаю (Like I don’t know).