So I’ve read and noticed that Japanese speakers regularly switch from using だ to です and using both plain and 〜ます forms very frequently throughout a conversation even with friends. Why is there such a common change in formality with people you’re close with or know well? And how do they decide which to use when?
Edit: I don’t mean transitioning permanently, I mean in everyday conversations where the switch is random. I have a friend who switches all the time while we talk and I’ve seen street interviews where the formality is completely all over the place. Why does it switch so often?