"They could have passed more than once."

Translation: Loro sarebbero potuti passare più di una volta.

[olegych76]

another senseless sentence that only confuses, and hindures learning.

[peter2108]

A previous sentence was Hai detto che non avrei mai potuto vincere (you said that I never could have won). That has avere + past participle + infinitive. But this sentence has essere + past participle + inifinitive. Can one use either, or is their reason for the difference?

[tanataviele]

as a matter of fact, Italians DO use both in this case

[peter2108]

f.formica answered this (see his stream). He gave http://www.zanichellibenvenuti.it/wordpress/?p=4610 as a reference. In Italian but quite staightforward.

[tanataviele]

nice link, and it says that 'avere' is acceptable too: 'Nel linguaggio corrente è largamente ammesso con i verbi intransitivi che vorrebbero l’ausiliare "essere" l’uso dell’ausiliare "avere", quindi: "ho dovuto andare", "avremmo potuto partire" non sono del tutto sbagliati."

[quindiquindi]

my question exactly!

[nictheman]

The general rule is that if it involves motion, or going from one place to another (like andare, venire, arrivare, or in this case passare) you should use essere, otherwise you should use avere. There are of course exceptions to this rule (such as reflexive verbs using essere) but when in doubt, essere->movement, avere->everything else