When do I use the subjunctive instead of the present indicative tense?

The present subjunctive is used in situations that express doubt and uncertainty. Things that you are to some extent unsure they will happen, unlike the present, used for true facts and situations. There are two specific situations in which the subjunctive is used that you need to know at A level: 1. In set phrases that use QUE which express desire, doubt or alternative: Bien que, Pourvu que, Il est possible que... All of these would be followed by subjunctive because the situation isn't sure. These are very useful in essays to introduce counter arguments. 2. Speech verbs such as: croire, dire, penser... ONLY when in negative form or question format: je ne pense pas qu'il sache tout sur l'histoire, pensez- vous qu'il sache tout? Even though these verbs do introduce opinion, you must remember they don't normally take the subjunctive, as it is a trap examiners like to use in A level papers.