When and how do I use the subjunctive?

The subjunctive is a tense that is used when there is an element of doubt or uncertainty.

Before looking at when the subjunctive tense is used, it would be useful to look at how verbs are conjugated in the subjunctive. Here, we shall only discuss how regular verbs become subjunctive. Irregular verbs (of which there are few and will be easy to remember) do not follow the same rules as regular verbs when becoming subjunctive. It works like most other tenses; with a stem of the verb, and endings for each person. We will use verbs with the ending RE as our example. The subjuntive "stem" for all regular verbs is simply the "ils" form, with it's ending removed. E.g the stem for the verb "vendre" (to sell) becomes "vendent" in the "ils" form and therefore it's stem for the subjunctive tense is "vend" as we remove the "ent".

Now we must look at the new ending to add in order to make it subjunctive. All regular verbs in the subjuncitve will take the "ER" present tense verb endings which I'm sure you'll be familiar with. ER verb endings:

Je = e

Tu = es

Il/Elle = e

Nous = ons

Vous = ez

Ils/Elles = ent

Now we can take our original stem of "vend" and add one of the endings above in order to form the subjunctive. E.g "Je vende" (I sell) would be written after a phrase triggering the subjuncitve tense. Now more on when the subjunctive is to be used.

 It's important to start with an understanding of the most obvious situations where the subjunctive would be used. Remember, it is only used when expressing uncertainty. 

E.g. "Je doute que" (I doubt that) is a phrase that would require the next verb in the sentence to be conjugated in the subjunctive. An example of how the sentence would finish is:

 "Je doute qu'il vende des pommes" (I doubt that he sells apples)