use of infinitive in a sentence where the subject is unchanged

Question

Since he made an effort to speak to me, I thought I should at least know his name.

'Puisqu'il a fait un effort de me parler, je croyais au moins devoir savoir son nom'

I am wondering if: a) I have used 'devoir' correctly since the subject of the sentence is still 'Je/I' and would therefore have no need to say 'Je croyais que ... je dois/devrais...' b) 'faire un effort' is the correct idiomatic equivalent of 'making an effort.' c) The adverb 'au moins' is correctly positioned in the sentence

Answer 1

Your sentence is correct, but heavy: the action is a chain of 3 verbs: croire, devoir, savoir. You might have rather turned it this way:

Puisqu'il a fait l'effort de me parler, je me suis fait un devoir de connaitre son nom.

Answer 2

a) It is hard to use the infinive devoir here.

b) yes

c) yes

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Je croyais au moins devoir savoir son nom won't be understood.

Here is an idiomatic way to say it:

Puisqu'il avait fait l'effort de me parler, je me suis dit qu'il me fallait au moins connaître son nom.

or

..., je me suis dit que je devais au moins apprendre son nom.