Preterite vs imperfect

Why is “El mundo cambío." in the preterite? That seems like something that happened over an undefined amount of time, so I would have thought imperfect.

¡Hola Scott_C!

Thanks for your question! 

A key difference between the preterite and the imperfect in Spanish is that the preterite indicates a completed action - something that both started and stopped in the past, and that is now over. We may not actually know the exact start and stop dates for this action, but the essential part is that we know that this action definitely ended in the past. The imperfect, on the other hand, generally shows ongoing past actions - ones where the stop and start are irrelevant, because the focus is just on the fact that at the (past) point in time being described, these actions were in progress.

So in the sentence El mundo cambió “The world changed,” the preterite is being used because the action of changing stopped at some point in the past. If we were to use the imperfect and say El mundio cambiaba instead, this would mean “The world was changing” and our focus would instead be on the fact that at a certain time in the past, this change was in progress.

I hope that helps! Do let me know if you still have any questions. If you'd like to read some more about the preterite vs. the imperfect, the section titled “Which Past Tense Should You Use?” in Lesson 10.6: “Action in the Past: 'El imperfecto'” has a nice breakdown.

Saludos,

Liss

That makes sense, thanks Liss!