'Il dottor Rossi': why Italian titles take an article
In English you say Doctor Smith is here or Mrs Jones called, with no article in front of the title. Italian does it differently. When you talk about someone using a title and their name, the title takes the definite article: il signor Rossi, la dottoressa Bianchi, l'avvocato Ferri, il professor Conti.
The article only disappears when you speak to the person directly: Buongiorno, signora Neri! English speakers tend to leave the article out everywhere, because that feels natural in English. This produces sentences like Dottor Rossi arriva, which sound wrong to Italian ears.
Think of it as two situations. In the first, you mention a person in the third person: you tell someone that the doctor is coming, or you say you have an appointment with the lawyer. Here the pattern is article + title + name. In the second, you address the person face to face, on the phone or in an email. Here you use only the title and the name, and the article goes away.
A useful rule of thumb: if you could replace the title and name with lui or lei, you need the article. If you could replace them with Lei (formal you), you don't.
The most common ones are signore and signora. Before a name, signore loses its final vowel and becomes signor.
Dottore and professore are shortened to dottor and professor before a name. Their feminine forms dottoressa and professoressa never change. Maestro and maestra, used for primary school teachers and for music conductors, keep their full form. Children often use the first name: la maestra Lucia.
These titles start with a vowel, so the article becomes l': l'avvocato, l'avvocata, l'avvocatessa, l'ingegnera. Ingegnere is shortened to ingegner before a name.
Presidente, vicepresidente, ministro, senatore, capitano and capitana follow the same pattern. When speaking directly to the person, the title is often used on its own.
Principe, principessa, barone and baronessa also take the article, usually before a first name or a family name.
The article merges with prepositions as usual, so you will often hear dal, al, della and similar forms in front of a title.
Remember the shortened forms: signor, dottor, professor, ingegner. You use them only before a name. On its own you say il dottore and il signore. When speaking directly to someone without a name, the full forms are used too: Scusi, dottore!
There is some variation in formal and informal style. For women lawyers, avvocata is now common and neutral, while avvocatessa can sound old-fashioned. In everyday speech, especially in the south, dottore is often used as a polite title for anyone with a degree. A few religious titles, such as don and suor, never take the article.
Talking about someone? Use the article: il signor Rossi, la professoressa Neri, l'avvocato Ferri. Talking to them? Drop it: Signor Rossi, come sta? Also remember to shorten signore, dottore, professore and ingegnere when a name follows.