In the dialogue for lesson 8.3 there is the sentence: 

Hi,

It's called apocope. Italians lop the vowel off the end of certain words like avere and dovere under certain conditions to, in their view, sound better. In my view it sounds good either way but they say that "aver perso" sounds better than "avere perso". There are certain cases where it is obligatory.

I googled and found a pretty good explanation: http://forum.wordreference.com/threads/apocope.384257/. 

Cheers,
Drew

Thanks Drew!  That would be a good topic to be covered in one of the grammar lessons - didn't see it in Level 2.

Have a great new year!
Jay

Hi Jay and Drew,

You can't have a conjugation after di, so the verb is in its infinitive form. Drew is right about the apocope: avere becomes aver so that the sentence sounds better. Some combinations are more common than others, and less common apocopes are often found in poetry ("Nel mezzo del cammin(o) di nostra vita [...] Ahi quanto a dir(e) qual(e) era è cosa dura [...] che nel pensier(o) rinova la paura", from The Divine Comedy).

Buon anno a entrambi! :)
Lucia

Thanks Lucia.  Didn't realize that you couldn't have a conjugation after di.

For the sentence:  "Credo di aver perso uno dei miei bagagli," could it have been written "Credo che ho perso uno dei miei bagagli" and translated as "I believe that I have lost a piece of my luggage" or does the  verb "credere" have to be followed by "di" if it is followed by another verb that doesn't use a subject?  

Buon anno anche a te!
Jay

You can only have a past participle that acts as an adjective, as in niente di sentito or niente di visto, literally "nothing heard", "nothing seen", the same construction of nothing new under the sun, niente di nuovo sotto il sole.

Otherwise, where a verb + di is present (penso di, capisco di, sentono di, ritiene di...), only the infinitive is used:
(Io) Penso di aver perso il portafoglio. I think I have lost my wallet.
Marco crede di essere simpatico. Marco believes he is nice.

If you use che, you'll need to use the subjunctive mood, otherwise the sentence sounds like fingernails on a chalkboard!

But:
When the subject is io, I, and the subject refers to itself, only di is possible:
Credo che io abbia perso uno dei miei bagagli.
The subjunctive is there, but the sentence still sounds terrible. Credo di aver perso... is the accepted translation.

When the subject refers to another object, che is the only way to go:
Credo che l'addetto abbia perso uno dei miei bagagli.
I believe the operator has lost a piece of my luggage.
Cerchi Marco? Credo che sia appena uscito.
Are you looking for Marco? I believe he's just gone out.

Credo che ha = credo che abbia...
Credo che è = credo che sia...

You'll find the subjunctive case later on in the course as it's not the easiest piece of cake to swallow.

If something is not clear, don't hesitate to ask!

Lucia

Thanks so much Lucia - that helps a lot!