Perhaps the greatest document addressing this question is Plato's "Sophist." Therein, Plato demonstrates that the ability to reason well amounts to knowing which of the most general classes of things go together. He compares this ability to musical ability, or knowing which notes harmonize with each other. The imposter can only repeat specific combinations, lacking as he does knowledge of the underlying structure.
> Then he who is able to do this has a clear perception of one form or idea extending entirely through many individuals each of which lies apart, and of many forms differing from one another but included in one greater form, and again of one form evolved by the union of many wholes, and of many forms entirely apart and separate. This is the knowledge and ability to distinguish by classes how individual things can or cannot be associated with one another. [Sophist, 253d]
> Then he who is able to do this has a clear perception of one form or idea extending entirely through many individuals each of which lies apart, and of many forms differing from one another but included in one greater form, and again of one form evolved by the union of many wholes, and of many forms entirely apart and separate. This is the knowledge and ability to distinguish by classes how individual things can or cannot be associated with one another. [Sophist, 253d]