(someone) thought (something) had (happened)

English has not only a past tense, but also something called past perfect ("had ___ed" or "had done"). It's a kind of "double past". We use it to talk about something that happened before a certain time in the past. For example, you can explain what you thought last night:

I thought he had left already.

You thought (in the past) that he had left already (before the time when you thought that).

This phrase appears in these lessons: