"Vous devez être un homme."
Is this being said like "You must be a man, because you have a deep voice" or like "You have to be a man, you don't have a choice"
isn't vous devez used for plurals? you(plural) have to be a man(singular)?
Vous can be both plural and singular. Plural when addressing a group of people. Or singular when talking to a single person in a formal or respectful way (i.e. people you don't know, older people, etc).
Your example is possible, but a bit strange. Usually you want the numbers to match (plural to plural, singular to singular).
Thank you for clearing that up. It works the same way in italian, I just didn't realize it.
When you have a vowel following a consonant (vous deveZ Etre un homme), you connect the two, carrying the consonant's sound over in what's known as "liaison": http://french.about.com/library/pronunciation/bl-liaisons.htm Hope it helps!