Thanks. So, אם is the most common in daily use "in the streets". I have understood that there are differences between formal/unformal/higer register/lower register/ spoken/written in many languages. Now I wonder where the 'line' between them are in Hebrew. At work: Would you use common or higher registrer ? If two teachers at university wrote letters to each other, would they use common or higher? In the courtroom? At the airport? In school? Teachers in the synagogues?