Je lirai jusqu'à ce que je sois trop fatigue

Question

J'ai vu que quelqu'un dèja demandait ce question, mais je n'a pas vu un repose. Pourquoi est-ce qu'il n'y a pas un change à sujet dans the phrase suivante: je lirai jusqu'à ce que je sois trop fatiguée?

Céline Pickard · Accepted Answer

Bonjour Raymond,
It is correct that with some expressions, the infinitive is more elegant and preferable than using the same subject:
J'ai besoin de faire mes courses (que je fasse mes courses) = I need to do my food shopping. 
To add to Maarten's answer, in this particular instance (with "jusqu'à (ce que + [Subjonctif])"), using "je" twice here is far more elegant even with the 2 subjects being the same.
I hope this is helpful.
Bonne journée !

Maarten Kamp · Answer

Raymond,

I think the question you are asking may be ‘ why the subjunctive is used when there is no change in subject between the 2 clauses ‘, as clearly changing the subjects in either clause would significantly change the meaning of the sentence.

There are expressions that always require the subjunctive, and ‘ jusqu’à ce que …. ‘ is one of these. In these cases, there is no reason to ask ‘why the subjunctive’ - it is obligatory.

The previous discussion linked below discusses situations in which the ‘ 2 subject requirement’ may be either helpful to remember, or not applicable.

https://french.kwiziq.com/questions/view/2-subjects-subjonctif