They offer classes on various subjects.
They offer classes in various subjects.
Which is correct?
Searching google for "classes in/on various subjects" shows that both variants are used frequently.
But after changing "subjects" to e.g. "chemistry",
They offer classes on chemistry.
They offer classes in chemistry.
1st variant sounds a bit wrong to me. Is it not?
So what is the pattern here? Does "in" and "on" are equivalent here, or maybe be they have a slight difference in meaning, or something else?