Learn Portuguese (Portugal): É possível que o alarme soe, porque há um teste hoje. - It is possible that the alarm sounds, because there is a test today.

The phrase É possível que (It is possible that) expresses doubt or uncertainty. Just like the word caso (in case) that you are learning in this lesson, expressions of possibility trigger the present subjunctive mood for the following verb. That is why the normal present tense soa becomes the subjunctive soe.

What is the infinitive of the verb soe?

The infinitive is soar, which means to sound or to ring. Because it is an -ar verb, it takes an -e ending in the present subjunctive for the he/she/it form. Watch out: it looks very similar to suar (to sweat), which becomes sue in the subjunctive!

Why doesn't the subjunctive carry over to the verb há later in the sentence?

The subjunctive mood is only triggered for the specific clause linked to the uncertainty (the alarm sounding). The second half of the sentence, porque há um teste hoje, states a concrete fact (there is a test today). Therefore, it uses the regular present indicative verb há.

Could I use pode ser que instead of é possível que here?