# Why the need to use the Futur Antérieur form "aura fallu"?

Le voleur a pu s’en servir pour descendre le sac d’or. Il lui aura fallu un complice qui l’attendait en bas.

I’m not sure why the verb "falloir" needs to take the form of the Futur Antérieur "aura fallu" here, especially given how "a pu" and "attendait" strongly indicate a past event. The juxtaposition of the future and the past, so to speak, has me puzzled. I’m at a loss how to interpret this sentence.

Is it impossible to use any other conjugated form than "aura fallu" in the given context?

If you look here: https://fr.wikipedia.org/wiki/Futur_ant%C3%A9rieur_en_fran%C3%A7ais (yeah OK worst source ever, whatev'), you can see four uses:

• Something that will end for sure in the future

Il aura terminé ses devoirs dans une heure.

• Something in the future but before another thing

Quand j'aurai terminé mes devoirs, je viendrai manger.

• A supposition

Il n'est pas encore arrivé ? Il se sera arrêté en chemin.

... equals 'il s'est probablement arrêté en chemin', the futur antérieur is already a supposition in this use case, and I would add that the probability with the futur antérieur is high, it's not maybe, it's probably. You can still use peut-être, probablement, sûrement to precise the degree of probability, but without any of these words, there is a notion of high probability, in my opinion.

• An assessment, a summary

Sa vie entière n'aura été que joie et bonheur.

In your case, it's a supposition with a high probability, but indeed I feel it like it's another case not explained on Wikipédia: since there is a notion of probability in 'a pu', the sentence sounds even more like (not the translation but the meaning):

If he really used it (we don't know what 'it' is in your example) to take the bag, so he needed a partner waiting for him downstairs.

I feel it like: MAYBE he used it (the probability is here), and if so, he NEEDED a partner (no probability, it's a consequence of the first probability if this probability is true).

• Using the Futur Antérieur form to make an informed guess about a past event. Interesting. Merci. Commented Aug 4, 2016 at 8:18
• ...and since when is wikipedia the worst source ever ? I wonder. In my humble opinion, no need for the sidenote, though I didn't dare erase it myself. Your choice, Simon. (by the way, +1 for the overall analysis) Commented Aug 5, 2016 at 13:12