Just how sure are you?

Do the words "subjunctive mood" mean anything to you? If so, you've probably studied a foreign language! You've also probably spent, depending on your commitment to mastering it, many hours trying to figure out this darn expression of uncertainty that, for the most part, we don't bother to distinguish in English.

If you've gotten to that intimidating stage of studying the subjunctive, you've probably had a teacher chastise your for improper usage at some point. "You don't use the subjunctive there! You're stating a fact!" or, "You must use the subjunctive! It's preceded by an impersonal expression!" Your teacher, most likely a native speaker, grew up breathing in her language's logic of the subjunctive. Certain phrases imply certainty and others don't! Surely that's clear to you! (It certainly hasn't always been clear to me!)

But I've discovered something studying Italian. Italian speakers and Spanish speakers differ on what phrases indicate certainty. For example, in Spanish, you don't use the subjunctive when you say, "I think that..." but in Italian, you must. IE:
Spanish: "I think that it is a good idea." Boom. Done. Good idea.
Italian: "I think that it may be a good idea." Just my opinion, though.

So if your Spanish teacher always told you that you use the subjunctive when expressing an opinion, but not when you say, "I think" (duh!) and you were confused, and thought, "but aren't I expressing an opinion?" you weren't alone. The Italians agree with you.

On the other hand, Spanish speakers use the subjunctive when using the word "when". Obviously! You don't know when, or even if it's going to happen! How could you state it with certainty? The Italians, on the other hand are more sure.
IE:
Italian: "I'll call you when I get back to the house." I mean, I'm going home, so when I get there I'll call you.
Spanish: "I'll call you whenever it is that I may get back to the house." I don't know when it's going to be. In an hour. Tomorrow. Maybe never. Sorry. But I'll call you when it happens!

It's not obvious! (Which by the way, would be a phrase that requires the subjunctive... I think.) These two different but similar languages look at some of these situations differently, and it is reflected in their grammatical rules. So the next time you're chastised for your incorrect use of the subjunctive, politely inform your accuser, "It isn't clear!" but whether the next part of your sentence should be subjunctive or not.... for that you're on your own.