You easily understand the following sentence: "At most colleges and universities, a large number of students receive financial aid." But how do you manage to understand the sentence? How is the concept of "financial aid" represented in your mind? Do you have a prototype (perhaps for "student on financial aid")? Do you have some number of exemplars? A theory? Can you specify what the theory involves? What other concepts do you need to understand in order to understand "financial aid"?