Before I get started, some background, skip if you don't care: I am not formally educated in Spanish. I learned (and am still learning, but I can now say that I'm fairly fluent) it on my own as a second language with free YouTube lessons, personal study, and kind of jumping into it. I do have family that speaks the language, but most grammatical topics, including the subjunctive, were new things to me about a year or so ago. I say this because, if I do make a mistake, and someone were to correct me, I would welcome it. I hope it helps someone out there, though, this is just how I've taken to thinking about the subjunctive and I think it could help a little bit.
The topic at hand: the subjunctive. The big bad wolf. Everyone talks about it, right? How hard it is to master, how knowing it demonstrates mastery. How we English speakers ourselves say that it's too much, for being so rare in English. Well, the truth is, it's none of those things. It's actually fairly simple. I also think that learning "triggers" is a good way to get started, but the natural consequence is that learners keep looking for triggers without an actual understanding of why they "trigger" that mood. Let me explain…
We say that English doesn't use the subjunctive as much as Spanish does, and that's about true I think, but we fail to realize just how often we use it in English, too. And I think it's helpful to understand how it's used in English, to elaborate on how it might be used in Spanish. There are many parallels in English and in Spanish with the subjunctive, or at least just enough to understand how it is used at a basic level.
I am not religious, but let's look at this phrase: God bless you. We English natives all know it, right? Notice anything strange about it?
Why isn't it… "God blesses you"? That would make sense, grammatically, in almost any other circumstance. Well let's look at it like this, "God blesses Adam". That also makes sense, right? But what's the difference? The meaning, right? So, if I said, "God blesses you", I'm telling you something that he, in reality, does. I'm just stating a fact.
When I say, "God bless you", I'm imposing my will for God to bless you, of which I am uncertain/I have no way of knowing if he currently does or not. Spanish has this very phrase, "que dios te bendiga". That verb, bendecir, is to bless. And if I wanted to state that God does in reality bless you, I would say "dios te bendice". He does that thing. My will or lack thereof is irrelevant. It is a fact. I know it as a fact.
Let's look at another parallel, "if I were you". Some English natives might say, "if I was you", but I think most of us would agree that it kind of sounds wrong. Why? "Were" in this specific context indicates hypothesis, non reality, something that we do not know to be true. Spanish, also has a direct translation, "si yo fuera tú". If you ever want to say, "if I were to…" "if I had done X"… then use the imperfect past subjunctive.
One way Spanish is unique in the subjunctive (I think, maybe I'm missing something) is its use of it, when relating to what I think of as subjective impact. What does this mean? Something made me personally (or someone else) feel some type of way. The feeling is fact, the reason is uncertain. I don't know exactly how to explain this in as much depth, with as much English examples, because I think English doesn't use it like that, but here are some examples:
"It made me mad that you said that" "Me enojó que dijeras eso" (Subjuntive is past, because the action done to me is in the past)
"I'm glad (it gladdens me) that you're okay" "Me alegra que estés bien" (Again, subjunctive follows the present tense verb, remains also a "present" tense subjunctive)
"Me gusta que le guste" "I like that he likes it"
"Le encanta que yo la llame en la mañana antes de que trabajemos " "She loves that I call her in the morning before we work"
That last one is related to my last point. "I call" takes the subjunctive because it personally impacts "her" in an emotional way. "We work" takes the subjunctive, not because antes de que is a "trigger", but rather because whatever follows antes de que is the future, that hasn't happened yet, but at some point will, but when is not being specified. It is uncertain. When "we" do that is not being conveyed, nor is it meant to be conveyed in this circumstance. It is simply before something that will happen, happens.
For example, let's look at "antes de que's" inverted cousin, "después de que". This can either take subjunctive or not. But why? Because it can be used in the past or the future. I can say, "me llamó después de que llegué a la casa (important, the accent on llegué, this is the past)". "He called me after I got to the house". No subjunctive, because it happened, in reality. I could say, "mi hijo, báñate después de que llegues a la casa, esta noche iremos donde tu tía". "Son, bathe yourself after you get to the house, we're going to your aunt's tonight".
If I say this, it implies something in the future that hasn't passed yet, and we haven't specified when in the conversation, nor do we know when my son will get home.
I hope this helps and wasn't too long winded, and I hope overall that it's understood.