Meaning of "devoir" in compound tenses

Question

Can anyone explain what the difference between the passe compose and past perfect forms of devoir are? google translate shows them as being the same thing:

J'ai dû faire quelque chose -> I had to do something

J'avais dû faire quelque chose -> I had to do something

Similarly what is the difference between the future and conditional forms:

j'aurai dû faire quelque chose -> I should have done something

j'aurais dû faire quelque chose -> I should have done something

Thanks!

Accepted Answer

Hi Patrick,
The first two are correct, although I think the English should be for the second one -
I'd had to do something = J'avais dû faire quelque chose
 
We are a lot stricter with 'concordance des temps' in French. In English, it is often not respected. Comments from English speakers are welcome!
J'aurai dû faire quelque chose = I will have had to do something
A better example would have been in the third person for instance -
She will have had to do something = Elle aura dû faire quelque chose
indicating a supposition that must have happened in the past , sometimes translated in English by -
She must have done something
and the last one is correct.

Answer

Bonjour Patrick,My best suggestion is to review each of the links below:-https://www.lawlessfrench.com/grammar/devoir-lesson/https://www.cnrtl.fr/definition/devoirhttps://vitrinelinguistique.oqlf.gouv.qc.ca/22441/la-grammaire/le-verbe/construction-de-certains-verbes/emploi-des-verbes-devoir-et-se-devoirThis, I believe, will offer you the range of usage that you are looking for.Hope this helps,Bonne journéeJim

Answer

@Jim and @Cecile - thanks for the feedback and the links. The one on lawless for devoir and the associated description of mode verbs was very helpful. I had a similar question about pouvoir and the articles explained why I was struggling with it. Normally I use key words in english (will -> future, will have -> future perfect, would / should / could -> Conditional etc) to figure out which tense to use, but I couldn't get it to work for devoir and pouvoir. Yet another of those situations where you have to learn by heart. Thanks for your help.