How do you form subjunctives in French and when should you use them?

The simplest way to form any present subjunctive is to take the verb, conjugated in the present indicative and put it the third person plural. Let's take the verb 'finir' as an example. The third person plural in the present tense is 'ils finissent'. Once you have this simply remove the verbal ending 'ils finiss ent ' and add on the present subjunctive endings which are:

-e, -es, -e, -ions, -iez, -ent

You should notice that when doing this that some present subjunctive forms are identical to their present indicative forms, such as 'ils finissent'. The way to distinguish the two forms is simple: subjunctives are always preceded by the conjunction 'que'. This is because subjunctives always express a state of unreality such as a wish, a possibility or an obligation. To express such a state, the subjunctive must be followed with an indicative verb to indicate what the speaker is trying to convey. For example, for a wish you would say 'je desire que...', for a possibility you would use 'il est possible que...' and for an obligation 'il faut que...'. (These indicative phrases are necessary in English too!).

To recap, subjunctives are used to express something that is yet to, or may never happen. They must always be preceded with an indicative verbal phrase ending in 'que'. They are formed on the stem of the third person plural of the present indicative.