Elegant synonym for subject matter of a discipline?

Question

I am writing an essay on critical thinking. I am trying to find a word that allows me to separate the subject matter of a scientific discipline (i.e. chemistry, geology, etc.) from the underlying logic that comes with using or understanding the knowledge. >Once a fundamental knowledge of physics is obtained, doing chemistry simply becomes a matter of applying critical skills to the _________

Answer 1

Theory

Principle

Concept