Questions & Answers about Je crois qu'ils vont réussir.
In French, when a verb like croire (to believe / to think) is followed by a full clause (a new subject and verb), you normally introduce that clause with que:
- Je crois que... = I think / believe that...
- Je crois qu'ils vont réussir. = I think they are going to succeed.
Saying Je crois ils vont réussir without que is incorrect in standard French. Que is required to link the main clause (Je crois) with the subordinate clause (ils vont réussir).