In general usage, subjects should be listed in lower case.

• She is majoring in geography.
• He enjoys his mathematics course.

Exception: when you are describing a subject that is also a language, culture or religion, capitalize it.

• She is an English major.
• He is doing well in his Spanish course.

When a subject is being described by its official or short form name, course or program title, it should be capitalized.

• She teaches in the Department of Geography at Memorial.
• He is taking a course called Elements of Discrete Mathematics.