The subjunctive is a form of a verb that is used to show a level of feeling, or doubt; it is commonly used to discuss whether something will happen or not. In French, the subjective is also used when a sentence has two different subjects. For example, the sentence, 'I want her to come back' uses two different subjects and hence will need the subjunctive tense = 'Je veux qu'elle revienne'. The subjunctive has many tenses and is usually triggered after the use of certain verbs, such as 'vouloir que' (to want), 'avoir peur que' (to be afraid), and 'falloir que' (it is necessary that). To form the subjunctive, take the infinitive of any verb and replace the ‘er’ or ‘re’ with (-e -es -e -ions -iez -ent), or ‘ir’ with (-isse -isses - isse -issions -issiez -issent). However this pattern is not always applicable as there are many verbs which have irregular subjunctive forms and therefore you must learn/memorise these forms.