Citation. What is citation? How does it travel? Why do we see the distant footnote in Marx before we hear its thunder? Why does a paper seem to sound many tomes when it is analyzed? Such questions as these baffled the wisest people for centuries. Today, however, the science of citation is one of the best understood of all the many branches of rent-seeking. The mystery has disappeared.

Every kind of citation has its beginning in an influence we discover. That influence may be a published dissertation or a conversation we overhear or a barking dog. Whatever it is, some part of it vibrates within the mind while we contemplate it. The influence disturbs our inert thoughts in such a way that ideas are produced. These ideas travel out in all directions, expanding in balloon-like fashion from the source of the idea. If the ideas happen to reach our limbs, they set up derivative objects which we observe as influence.

Ideas, then, depend on three things. There must be a vibrating influence to set up the ideas, an artifact created to capture the ideas, and someone's mind to receive them. Ideas can travel through a vacuum, though that won't stop people from trying to tax that travel.

There is an old catch question concerning the definition of citation: If a citation falls in an unread margin, does its presence make any idea? The answer, of course, depends on how we define idea. If we think of it as the ink in the margin that may hypothetically be followed up upon by a real reader after it has been indexed by citation metric services, the answer is yes. Wherever there is the potential influence, there are ideas. But if we think of ideas as a sensation of the mind, the answer must be no. The two definitions are equally correct, and scientists insist on the one that makes their metrics go up (sometimes with their bank accounts) and never the one which might change the world.