What is the present subjunctive and when is it used?

The subjunctive is classed as a mood rather than a tense. Here we will address the present subjunctive; once you know avoir and etre you can use the perfect subjunctive.But for arguments sake, we will treat it as a tense. The subjunctive is used after certain (1) impersonal expressions, expressions of (2) doubt or (3) emotion, or (4) particular verbs. There are (5) certain conjugations which just always take the subjunctive (there is no reason, you just need to learn them).Some examples:1) Il faut qu'on fasse... (It's necessary that we so)Il est impossible qu'il aie raison... (It is impossible that he is right)2) Je ne suis pas sûr/e que ce soit une bonne idée... (I am not sure it is a good idea)Il n'est pas certain qu' il y ait... (It's not certain that there is)3) C'est dommage que...J'ai peur que...4) Aimer mieux que (only when que follows aimer)Souhaiter que...Demander que...Douter que...5) Avant que/ après que...Qui que (whoever)Quel/le/s que (whatever)When Que is at the start of a sentenceThere are other instances when the subjunctive is needed, these include all superulatives, certain negatives eg: Je n'aime pas que/ Je ne pense pas que... After phrases of premier, dernier and seul - eg: c'est la seule personne que je connaisse... Hypothetical thoughts also take the subjunctive, as they include doubt eg: Je cherche une voiture qui ne soit pas trop chère (you haven't bought the car, you're only thinking about it. This sentence would work the same if the fist part was conditional).Finally...How is the subjunctive formed?By taking the ils form of the present tense, removing the 'ent' eg: ils mangent and adding the relevant endings:Je - eTu - esIl/ elle/ on - eNous - ionsVous - iezIls/ elles - entSo, manger for ils in the subjunctive is the same - ils mangentIrregular verbs include: aller, avoir, etre, faire, falloir, pouvoir, savoir, valoir et vouloir(Some verbs are irregular in just the nous and vous forms eg: boire - nous buvions and vous buviez)