Use of subjunctive with jusqu’a ce que.....

Question

Ben restera assis à ce bureau jusqu'à ce qu'il ait fini ses devoirs.

Hi, can you please tell me why one uses the subjunctive in the above sentence. I thought that you only used the subjunctive if the subject of the main clause and the subclause were different. In the sentence above, they are the same.

Thanks

Sondy

Answer

There are quite a few different circumstances which demand the subjunctive such as sans que, au moins que, de peur que, avant que, etc., and also jusqu'à ce que.

What you are thinking of is probably that you can use a different construction, one avoiding the subjunctive, when the two subjects in the respective clauses is the same:

I doubt that I will come. -- Je doute de venir. But also possible: je doute que je vienne.

Answer

Read the discussion from Alan and Cécile below. There is no infinitive alternative when jusqu’à ce que is used - so it always needs the subjunctive. Many sites, including Lawless state the 2 subjects must  be different as a required condition,  but it seems that ignores exceptions ! I think Alan and Cécile are correct.  My wife (French) would definitely use subjunctive here.