What is the subjunctive?

The subjunctive is a verbal mode, a way that we can change a verb so that it expresses a certain meaning. Normally we use the indicative mode to indicate something certain or regular, e.g. "Je vais à l'école" = I go to school. We use the subjunctive mode when there is a meaning of doubt, uncertainty, wish, or emotion that we want to convey e.g. "J'aimerais que tu ailles à l'école" = I would like for you to go to school