To simplify the math and prove things we make some assumptions. Because we like rules and theories to be

clean and

universal, we describe their requirements as "

perfect".

Such a perfect market has:

The degree to which real markets adhere to these assumptions is generally the benchmark of their purity and correctness. Unhealthy markets do not exhibit one or more of these characteristics.

Of course, a really perfect capital market is one in which I, and I alone can break all those rules...