Is there any difference between the usage of "in" or "on" in terms of class?

I'm teaching a class in/on math(s). My father teaches a class in/on marine biology.

I have a class in French to go to tomorrow. I have a class on historical artwork that I love.

I take a class in physics. I'm not taking any classes on Spanish history this year.

The difference seems minimal, but it also seems to exist. For instance, "I'm not taking any classes on Spanish" sounds odd to me, as if to say you could take classes on Spanish as a whole language, and not as a student of the language, if that makes any sense.

Anyone have any idea what's going on with these two prepositions?

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    I think grammatically, both prepositions are acceptable and will work well. However, (a) the tendency to use on is catching on post-1950; (b) we can find many instances of mixed use by the same author in the same publication; (c) I myself use in for broader subjects ("in science") and on for specializations ("on advanced fluid dynamics") -- naturally? – Kris Feb 3 '15 at 12:59
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    Both sound somewhat awkward to me with maths and physics; I'd say maths class and physics class. To me, on implies that the class teaches knowledge about or relating to the subject, but the subject itself is not what you learn. You learn about Spanish history, but you don't learn the Spanish history; conversely, you do learn (the) Spanish (language) itself in a Spanish class, you don't just learn about it. The more the thing you learn is ‘metadata’ about the subject, rather than being the subject itself, the more likely I am to use on. – Janus Bahs Jacquet Feb 3 '15 at 14:33
  • In the case of language classes, in is ambiguous: class in French could mean that the class teaches the French language or that it's a class on some other subject that is taught in French. – Barmar Feb 3 '15 at 16:54
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    Note also that it's math in American English, maths in British English. – Barmar Feb 3 '15 at 16:55

The Chicago Manual of Style does not include the word "teach" in their list of common problematic words and the correct preposition construed with them. It does include the verb "instill," and indicates that this verb is correctly used with the preposition "in."

More interesting, though, is the inclusion of the word "based." It indicates that the following adjective should be "on" when used preceding a premise, and "in" when used preceding a field of study.

With this guideline, I would assume that the preposition used should be selected to convey either a summary of the class subject ("on"), or an immersion in the class subject ("in"). For instance, I would take a class in standard deviations if I was pursuing a degree in mathematics and had already acquired any prerequisite credits. Or, I might take a class on carpet-laying at my local community college; the class subject is limited and does not imply a broader range of study.

It stands to reason that common use may default to prepositional accuracy without much conscious thought on the part of a speaker. The preposition is likely considered further in written communication to convey credibility.

  • The reason that teach is not included in the problematic list, is that it is not problematic. You teach Spanish, you teach maths, you teach art history. The problem is class in/on. – Peter Shor Feb 4 '15 at 17:13

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