Dear Ann Landers,
the formal, which is used for elders, people of authority and strangers, and the familiar, which is used for friends, family and close associates. Using the familiar form to address strangers is a sign of disrespect or poor upbringing. In fact, this is the case in most European countries. Even now, after 40 years in the United States, I find it difficult to address casual acquaintances by their first names. And many salesmen never get past the first sentence when they use my first name. It's not because I am aloof; it's just a formality born of my native culture.

Dear Dr. M.,
Thank you for a letter sure to teach many people (including me) something useful today. If any of you readers are planning a trip to a Spanish-speaking country, or any foreign city for that matter, I suggest that you remember this column.