Passé composé + avant que : Why subjonctif? It seems very factual (vs doubt)

Question

As I see more examples with the subjunctive, I’ve been trying to get the feel for the sense of the usage rather than relying on memorizing the patterns. One example though eludes me as to where the sense of doubt is coming from. In particular, the use of passé composé seems to remove the uncertainty. This statement seems rather factual vs the other examples in the exercise.
Tu es arrivé avant que je n'aie fini mes devoirs.You arrived before I finished my homework
Is there a way of interpreting this to get the sense of the subjunctive mood?

Accepted Answer

Some expressions just always take the subjunctive. It is not always obvious, predictable or explicable based on the ‘rules’ even if, in a round about way, it fits with them. Avant que always takes the subjunctive. I wouldn’t try to understand these and that is not the way native French speakers learn them either - better to “learn” them by acquisition in context as they come along. 
The link below might be helpful.
 
https://www.frenchtoday.com/blog/french-verb-conjugation/understanding-french-subjunctive/

Answer

Hi Jeff,Further to Maarten's point  --  the nearest aspect that occurs to me is an element of "emotion".The need to consider the potential effect of a particular (proposed) action -- it's all a bit speculative on my part though.Jim

Answer

Hi Jeff: For minimal "head scratching" go with Maarten. Some expressions de facto take the subjunctive! afin que;bien que;quoique etc etc.

Once you encounter and learn to identify these expressions, then go with JIm's "potential effect" "element of emotion" to try and get why the subjunctive. Hint... these conjuctive expressions often add an emotion of negative or contrary reaction or put a purpose/condition on the "favour" of the main clause.

Now to directly accept your challenge. What if I said "Man! You arrived before I finished my homework"! Pretty subjective (and contrary) reaction to your early arrival eh. Still , as Maarten said, for that particular sentence you would have had to recognize the expression"avant que" first.

Answer

Hi Jeff: For minimal "head scratching" go with Maarten. Some expressions de facto take the subjunctive! afin que;bien que;quoique etc etc.

Once you encounter and learn to identify these expressions, then go with JIm's "potential effect" "element of emotion" to try and get why the subjunctive. Hint... these conjuctive expressions often add an emotion of negative or contrary reaction or put a purpose/condition on the "favour" of the main clause.

Now to directly accept your challenge. What if I said "Man! You arrived before I finished my homework"! Pretty subjective (and contrary) reaction to your early arrival eh. Still , as Maarten said, for that particular sentence you would have had to recognize the expression"avant que" first.

Answer

Answer

Hi Jeff: For minimal "head scratching" go with Maarten. Some expressions de facto take the subjunctive! afin que;bien que;quoique etc etc.

Once you encounter and learn to identify these expressions, then go with JIm's "potential effect" "element of emotion" to try and get why the subjunctive. Hint... these conjuctive expressions often add an emotion of negative or contrary reaction or put a purpose/condition on the "favour" of the main clause.

Now to directly accept your challenge. What if I said "Man! You arrived before I finished my homework"! Pretty subjective (and contrary) reaction to your early arrival eh. Still , as Maarten said, for that particular sentence you would have had to recognize the expression"avant que" first.