Let me
give an example. The fact about to be stated, was communicated to me by
a gentleman of eminent commercial standing in Philadelphia, at that time
the President of one of its leading banks. The fact occurred in his own
personal experience. He was, at the time of its occurrence, largely
engaged in the cloth trade. His faculties of mind and body, and
particularly his sense of touch, had been so trained in this business,
that in going rapidly over an invoice of cloth, as his eye and hand
passed in quick succession from piece to piece, in the most
miscellaneous assortment, he could tell instantly the value of each,
with a degree of precision, and a certainty of knowledge, hardly
credible. A single glance of the eye, a single touch, transient as
thought, gave the result. His own knowledge of the subject, in short,
was perfect, and it was rapidly winning him a fortune. Yet when
undertaking to explain to a younger and less experienced member of the
craft, whom he wished to befriend, by what process he arrived at his
judgment, in other words, to teach what he knew, he found himself
utterly at a loss. His thoughts had never run in that direction. "Oh!"
said he, "you have only--to look at the cloth, and--and--to run your
fingers over it,--thus. You will perceive at once the difference between
one piece and another." It seems never to have occurred to him that
another man's sensations and perceptions might in the same circumstances
be quite different from his, and that in order to communicate his
knowledge to one uninitiated, he must pause to analyze it; he must
separate, classify, and name those several qualities of the cloth of
which his senses took cognizance; he must then ascertain how far his
interrogator perceived by his senses the same qualities which he himself
did, and thus gradually get on common ground with him.

Let the receiving-teller of a bank be called upon to explain how it is
that he knows at a glance a counterfeit bill from a genuine one, and in
nine cases out of ten he will succeed no better than the cloth merchant
did. Knowing and communicating what we know, doing and explaining what
we do, are distinct, separable, and usually very different processes.

Similar illustrations might be drawn from artists, and from men of
original genius in almost every profession, who can seldom give any
intelligible account of how they achieve their results. The mental
habits best suited for achievement are rarely those b