There are no differences in meaning, just differences in how you might use the phrases in a sentence. For example if talking about literary theories you could use both just for variety, e.g. 'Today we are going to discuss theories of literature. Now, as I am sure you are aware, there are several schools of thought within the field of literary theories...' And so on. It's about how each phrase sounds/fits within a sentence, varying the two to avoid too much repetition. The meaning however is the same.