The subjunctive is classified by grammarians as a mood, not a tense. Tense refers to what time a verb takes place, mood refers to the attitude of the speaker toward the action. The moods in French are the indicative, the infinitive, the subjunctive, the conditional, the participial, and the imperative. The indicative mood, for example, refers to statements that refer to facts:
-La France est en Europe. (France is in Europe.)
Here est represents the indicative.
The subjunctive, however, refers to statements that are contrary to fact or highly subjective in nature:
-Il est possible que la France soit le plus grand pays de l'Europe occidentale. (It is possible that France is the biggest country in Western Europe).
In this case, soit is used instead of est, because the statement expresses possibility, not fact. The speaker is not certain that France is the largest country, he or she is merely recognizing the possibility.
The subjunctive mood has two major uses: obligatory and optional. The obligatory subjunctive is found in subordinate clauses which follow certain expressions, as in the example above. "Il est possible que..." is a phrase which requires the subjunctive clauses which follow it. Some expressions, such as "je crois que..." require the subjunctive only when used in a negative or interrogative sense.
-Je crois que la France est belle. (indicative)
-Je ne crois pas que la France soit belle. (subjunctive)
-Croyez-vous que la France soit belle? (subjunctive)
The second two sentences are a negative statement and a question, respectively, and therefore the verb in the subordinate clause is in the subjunctive mood rather than the indicative.
In the optional subjunctive, the speaker has the choice of using the indicative or the subjunctive in order to express whether or not the statement refers to fact. Example:
-Je cherche un restaurant qui est près d'ici.
-Je cherche un restaurant qui soit près d'ici.
The first sentence implies that I'm looking for a specific restaurant which I have been told is nearby; the second sentence, using the subjunctive, implies I'm trying to find out if there is a restaurant nearby.
There are four tenses in the French subjunctive, the present, the past, the imperfect, and the pluperfect.