Are You Hypothesizing With 'Supposer'? Then Use the French Subjunctive

When supposer ("to suppose" or "to assume") is used with a dependent clause beginning with que, the dependent clause may use a subjunctive verb, depending on how supposer is used.

When it expresses an assumption, no:
   Je suppose qu'il le fait.
   I assume that he is doing it.

When the subject is presenting a hypothesis, yes:

   Supposons qu'il le fasse.
   Let's suppose that he does it.

Supposer que joins a long list of similar verbs and expressions of doubt, possibility, supposition, and opinion; they all also need the subjunctive in the ​que subordinate clause.

'Supposer' and 'Supposer Que'

Supposer que, when used to express an hypothesis, fulfills the subjunctive's underlying requirement of expressing actions or ideas that are subjective or otherwise uncertain.

As with this use of supposer que, the French subjunctive is nearly always found in dependent clauses introduced by que or qui, and the subjects of the dependent and main clauses are usually different, as in:

   Je veux que tu le fasses.
   I want you to do it.

   Il faut que nous partions.
   It is necessary that we leave.

French Verbs and Expressions Similar to 'Supposer Que'

Here are other verbs and expressions that, like supposer que, can communicate doubt, possibility, supposition, and opinion. They all require the subjunctive in the dependent clause that begins with que. There are many other types of constructions that need the French subjunctive as well, which are explained and listed in the full-on "subjunctivator" (our term).

• accepter que > to accept
• s'attendre à ce que > to expect that
• chercher ... qui* > to look for
• détester que > to hate that
• douter que** > to doubt that
• il est convenable que > it is proper/fitting/appropriate that
• il est douteux que** > it is doubtful that
• il est faux que > it is false that
• il est impossible que > it is impossible that
• il est improbable que > it is improbable that
• il est juste que > it is right/fair that
• il est possible que > it is possible that
• il est peu probable que > it is not very likely that
• il n'est pas certain que > it is not certain that
• il n'est pas clair que > it is not clear that
• il n'est pas évident que > it is not obvious that
• il n'est pas exact que > it is not correct that
• il n'est pas probable que > it is unlikely that
• il n'est pas sûr que > it is not certain that
• il n'est pas vrai que > it is not true that
• il semble que > it seems that
• il se peut que > it may be that
• le fait que > the fact that
• nier que*** > to deny that
• refuser que > to refuse
• supposer que > to suppose / assume; to hypothesize

*When you are looking for someone who may not exist, this indicates doubt and therefore requires the subjunctive in the dependent clause:

   Je cherche un homme qui sache la vérité.
   I'm looking for a man who knows the truth.

**These do not take the subjunctive when they are used negatively:

   Je doute qu'il vienne. > I doubt he's coming.
   Je ne doute pas qu'il vient. > I don't doubt he's coming.

***When nier is in the negative, it's followed by the the more formal ne explétif, which uses only ne (without pas).

   Il n'a pas nié qu'elle ne soit partie.
   He didn't deny that she left.

Additional Resources

The Subjunctivator
Quiz: Subjunctive or indicative?