Knowing

To find out whether or not a person knows a concept, there are several approaches possible. My favorite method which I think is the most complete, is to let the person explain about the concept.

To explain a concept, one has to be familiar with not only the identities and the phrases that refer to them, but also the mechanisms of how the identities interact. In short, one has to know the words, things involved, and how they interact. And being fluent with the above can assure that the person can answer any questions regarding the subject, since all the answers to a question related is simply one of diverse combinations of the concepts involved.

If you can’t explain it simply, you don’t understand it well enough – Albert Einstein

p.s. Knowing a concept well and applying it somewhere analogous is sadly a different matter. It needs a different set of skills, which would be pattern recognition in terms of finding some concepts that feel similar.