Which auxiliary verb is used with compound tenses that combine modal verbs and reflexives?

Question

To conjugate verbs in the passato prossimo (and other compound tenses) where a modal verb is needed the following formation is required:

AUXILIARY VERB (avere or essere) + MODAL VERB (past participle form) + INFINITIVE

The rule for determining which auxiliary verb to use is determined by the infinitive (as opposed to the modal verb) Take for example the following:

Ho potuto comprare un biglietto (I was able to buy a ticket)

as well as:

Sono potuto andare al cinema (I was able to go to the movies)

The difficulty arises when looking at reflexive verbs that universally require essere as an auxiliary verb. For example:

Mi sono svegliato alle 6.00 di mattina. (I woke up at 6 in the morning.)

When you add a modal verb to this structure, how is it correctly rendered?

Is it:

1. Ho dovuto svegliarmi

or

2. Sono dovuto svegliarmi

If the first example is correct, why does it not follow the rule that the auxiliary verb is determined by the infinitive 'svegliarmi' as it normally is?

Answer 1

In theory both forms are correct (see below), but in this case, in my opinion, it is by far more usual to say:

Mi sono dovuto svegliare

This can be generalised. Quoting Serianni:

Se il verbo servile regge un infinito pronominale, cioè combinato con un pronome atono, l'ausiliare del verbo reggente sarà essere se il pronome è anticipato (non ci sono potuto entrare), essere o avere se il pronome è posticipato (non sono potuto entrarci o non ho potuto entrarci).

i.e.

If the modal verb is followed by an infinitive with a pronoun [as svegliarsi in your example], the auxiliary verb for the main verb is essere if the pronoun is put before the verb (non ci sono potuto entrare), and either essere or avere if the pronoun appears after the verb (non sono potuto entrarci o non ho potuto entrarci).