Addressing a professor - culture clash I am a Ph.D. student in a country where everyone is addressed by their first name (professors etc.). I call my advisors by their first names and when we have visitors in our research group I go by this rule. However, now I am visiting a German university and I don't really know how to address the professor who has invited me. Before my stay, I would call him by his first name - but now that I have met him at his university and his Ph.D. students (who seem to call him Prof. X) I am becoming unsure about it. Consequently, I have been very inconsistent with how I have been addressing him.

My questions are:


should I apologize for being inconsistent/possibly being rude? Or am I overthinking this?
how should I address him?
A lot of us who live in both worlds (I am German and frequently visit there, but live and work in the US), we call colleagues we don't know well by their first name when we meet in the US, and by Professor X when we meet in Germany. In other words, we use the common convention of the place we're in. That's probably a good rule for you to live by as well.