I left before they had decided what to do.
Is this because this is a past version of "I leave before they have decided what to do"?
Because "left" doesn't come before "decided".
past-perfectpast-tensesimple-past-vs-past-perfect
I left before they had decided what to do.
Is this because this is a past version of "I leave before they have decided what to do"?
Because "left" doesn't come before "decided".
Best Answer
There is a meaning distinction between these:
The first one can have the nuance: I left specifically not to be there when they decide. The second one does not, and that form with the perfect would be used when the speaker wants to make it clear "I left before they decided, but not in order to avoid their decision".
This is essentially what the perfect aspect is doing, and is probably the reason why it doesn't matter that "to leave" takes place before "to decide". The point is that the action of leaving takes place before the the action of deciding is complete, i.e. perfect! "I did not run away to avoid the decision-making; I was just not there when that action completed". The completeness is expressed using the perfect aspect, and since this is all in the past it becomes the past perfect: the timing of a simple past is compared to the time of completion of a past perfect.
Perhaps these examples can make the semantic side of it clearer:
What is the present version? In modern English we don't use forms like "now I eat breakfast" or "I go to work". These come across as archaic. Rather, the gerund forms are used -- unless it is about habitual performance, such as "I usually eat breakfast just before I go to work". This does not apply to one time actions or actions at the moment. So the present tense of your sentence is this:
And it means: I am leaving, and as I leave, they are still undecided..
If we remove the perfect, it changes:
And now it it means: I am leaving specifically not to be there when they decide what to do.
The past tense doesn't strictly have the "in order to" nuance, but the present does.
Lastly note that forms like "I am leaving before they have decided" are not that common in everyday speech. This sounds very contrived; perhaps one might use it in a letter or other writing. It has the air of a detached commentary on the situation. It's better said like "I'm leaving them undecided"; "They are still undecided as I'm leaving"; "They haven't decided though I'm already leaving"; and similar.