German is no longer a commonly studied language in America, which is a great pity, given its power and scope. One interesting and rather quaint feature of traditional German onomastic practice is addressing the wives of men who bear the academic titles “Doctor” and “Professor” as “Frau [Mrs.] Doktor so-and-so” and even “Frau Professor Doktor so-and-so.” (Note that “Professor” precedes “Doctor.”)
In contemporary American academe, there is a strange bifurcation in the use of the titles “Dr.” and “Professor” whereby students and teachers in junior, community, and state colleges––notably in the rural South and the Southwest, where this also applies to private institutions––typically use only “Dr.” for designees with doctorates, even when the person so named/addressed is of professorial rank, whereas in Northern private (esp. elite) universities the habitual appellation is “Professor.” This bifurcation seems to apply, for instance, even when the person addressed is a private university professor, so long as the colleague speaking is from a Southern institution. Thus I am routinely addressed/referred to by former students who now teach at Southern universities as “Dr. Shapiro.”
Some narrowly literal-minded academics withhold the title “Professor” from persons who do not occupy professorial positions at the time when they are being addressed. A grotesque instance (remembered here from bitter experience) is the treatment of my late wife––the most accomplished and versatile American Italianist of the twentieth century–– by a nincompoop of a male colleague, who referred to her as “Professor Shapiro” only so long as she was teaching and held professorial rank, but stripped her of this title whenever she was between jobs, at which times he invariably referred to her as “Dr. Shapiro.”
A final personal sidebar, for the nonce: one of my oldest and dearest friends, an eminent prosthodontist, always introduces me as “Dr. Shapiro.” Coming from him, I take this as a special mark of honor and respect. After all: any fool can be a professor––but not a doctor.