"He was incredible yesterday"

Question

I translated this as 'Il était incroyable hier' - but it was marked wrong, citing the correct answer as, 'Il a été hier'    why? Even when I put it into a translator it says it should be était. What am I missing?

Answer

Matt,

This touches on a complicated topic that takes time to come to grips with, and one that is not easily differentiated by online translators.

Context is important, as either passé composé or imparfait could be used here, depending on meaning being conveyed. To be fair to DeepL at least, it gives both tenses as alternatives for ‘ he was incredible yesterday ‘, and can’t be expected to do more than that for this as a stand alone sentence.

If the question was part of the lesson you linked, then the context is firstly that it is testing understanding of conjugation of être in passé composé, and more importantly in the bigger picture, that a specific time period is given for this ‘ event/action ‘ of ‘ being incredible ‘ - it was something notable that ‘ happened yesterday ‘.

Have a look at the ‘ Bonus ‘ section of the first attached lesson for an example that can be imparfait or passé composé, and the difference in meaning.

The 2nd link is one of the best descriptions of practical usage of imparfait or passé composé that I have found. The little videos at the end are worth watching too.

Using the compound tense (Le Passé Composé) on its own or with the imperfect tense (L'Imparfait)

https://www.frenchtoday.com/blog/french-verb-conjugation/passe-compose-versus-imparfait/