Learn French: Nous doutons que les concurrents fassent des bénéfices. - We doubt that the competitors make a profit.

The phrase douter que (to doubt that) expresses uncertainty, which is a classic trigger for the subjunctive mood in French. Therefore, we must use the subjunctive form of faire (fassent) instead of the indicative (font).

How do we get the form fassent?

Faire is completely irregular in the subjunctive. Instead of using the normal present tense "ils" form as a base like regular verbs do, it uses the special stem fass-. Since les concurrents is a plural "they" subject, we add the standard subjunctive ending -ent to get fassent.

I know douter que takes the subjunctive, but what if the sentence used se douter que?

This is a very common trap! While douter que (to doubt) takes the subjunctive because of the uncertainty, se douter que means "to suspect" or "to guess." Because it expresses a strong belief that something is true, se douter que is followed by the normal indicative, not the subjunctive.

Why does the French sentence use des bénéfices (plural) when the English translation says "a profit" (singular)?

In French, the standard expression for a business making money is faire des bénéfices (literally "to make benefits"). It is typically used in the plural in French, even when we translate it as the singular "to make a profit" in English.