Which day is referred to by someone using the phrase "this Monday" vs the day referred to when using "next Monday"?
I have always used "this Monday" to mean the coming Monday, or the next Monday to occur on the calendar. So, if it is Tuesday and I say "I will be ready for this Monday", I mean I will be ready on Monday the following week. "next Monday", then, refers to the second Monday occurring on the calendar in my usage.
Is there a rule or generally accepted principle on this?
This is a very big problem, and I'm not sure that native English speakers even understand how big it is.
Yes, if I were talking with my wife tonight about a class I'll teach on October 30, I'd say, "This Monday I'm teaching the Outdoor Rec students." I could also say, "This Monday the Rec students were crazier than usual." And my wife would understand I mean the Monday of the present week.
The key here is the verb tense. If I say, "This Monday I'm teaching" or "This Monday I'll teach," I mean the next Monday on the calendar. If I say, "This Monday I taught," I mean the most recent Monday.
But...I could also say, "Next Monday I'll teach," and my wife would understand I mean October 30. "This" and "next" seem to be roughly synonymous. If I wanted to be more precise, I could say, "This Monday [October 30] I'll teaching the Rec students, and the next Monday I'll teach the Tourism students."
"The next" tells her that it's the following Monday. But I have no idea why we need "the" to identify that following Monday.
It's even worse in Britain. They're quite accustomed to saying, "I'll teach Monday next" (=the next Monday on the calendar). And they also say "I'll teach Monday week" (=a week from the coming Monday).
This is why people learning English as a second language say, "This Monday I'm switching to German, or Portuguese, or Turkish!"