Breakdown of J'ai peur que la marée monte.
je
I
monter
to go up
avoir peur
to be afraid
que
that (introducing a clause)
Questions & Answers about J'ai peur que la marée monte.
Why is there a que after peur in this sentence?
The phrase avoir peur que (to be afraid that) expresses a strong emotion. In French, expressions of fear, doubt, or desire trigger the subjunctive mood for the verb that follows.
Is monte in the subjunctive here? It looks exactly like the normal present tense.
Yes, it is the subjunctive! For regular -er verbs like monter, the present subjunctive endings for je, tu, il/elle/on, and ils/elles are identical to the normal present tense (the indicative). We know it is subjunctive here purely because avoir peur que grammatically demands it.
I sometimes see an extra ne after avoir peur que. Why isn't there one here?
You are thinking of the 'ne explétif'. In very formal French, you might read j'ai peur que la marée ne monte. This particular ne doesn't make the sentence negative; it just emphasizes the feeling of fear. However, it is completely optional and almost always left out in everyday or spoken French.