What is the difference between the preterite and imperfect tenses in Spanish? When would you use each?

The preterite and imperfect tenses have different conjugations, which it is necessary to learn by heart. In terms of usage, whilst they both refer to actions that have taken place in the past, they do have very different meanings. The preterite tense is used to explain completed actions in the past, that happened at a specified time and which lasted for a finite and defined period of time. The imperfect tense, on the other hand, is used to describe events and actions that were ongoing over a longer and not necessarily clearly defined period of time in the past. The imperfect tense can also be used to set out routines or repeated actions in the past - for example, what you did every day when you went to school, whereas the preterite is used to explain one-off actions and events. If you want to use both tenses together, you use the imperfect to describe what the situation was like at that particular point in the past e.g. 'it was raining' - the imperfect 'sets the scene'. The preterite, when used with the imperfect, explains intervening actions that took place against the backdrop set out by the imperfect - for instance, 'it was raining when I arrived' - here, your arrival is the action that cuts in over the backdrop. If you use the two tenses together, you can get a high mark for your GCSE writing assessments.