When should the subjunctive be used?

The subjunctive is a mood in Spanish which has its own grammatical endings and is generally used to express something that might be possible or that there is doubt about. The subjunctive can be recognised both by its grammatical endings which are different to the normal indicative and also the 'trigger' before the verb which causes it to be subjunctive.

A good example of the difference between the two is using 'aunque' which can mean both even if or even so depending on context.

Aunque llueva mañana, iremos al parque - Even if its raining tomorrow, we will go to the park.

Aunque llueve hoy, queiro salir - Even though its raining today, I want to go out

The first of these sentences takes the subjunctive as it is not known for sure whether it will rain tomorrow - there is an element of the unknown.

The second is stating a fact that it is is raining which is known - so the indicative is used.

There are many other subjunctive triggers which can be learnt so it can be easily recognised.