mount of deflection
it was mathematically calculated, prior to any further
observation, that the supposed planet should appear at a certain
point in space. It was by this deductive elaboration that
the planet Neptune was discovered. It was figured out deductively
that a planet deflecting the path of the planet Uranus
by just so-and-so much should be found at just such and such
a particular point in the heavens. When the telescopes were
turned in that direction, the planet Neptune was discovered
at precisely the point deductively forecast.

The elaboration of an idea through reasoning it out may
sometimes lead to its rejection. But in thinking out its
details we may for the first time note its appositeness to the
solution of the problem in hand. The gross suggestion may
seem wild and absurd, but when its bearings and consequences
are logically developed there may be some item in
the development which dovetails into the problem as its
solution. William James gives as the outstanding feature of
reasoning, "sagacity, or the perception of the essence."[1] By
this he meant the ability to single out of a complex situation
or idea the significant or key feature. It is only by a logical
development of a suggested solution to a problem that it is
possible to hit upon the essence of the matter for a particular
situation, to single out of a gross total situation, the key to
the phenomenon. "In reasoning, _A_ may suggest _B_; but _B_,
instead of being an idea which is simply _obeyed_ by us, is an
idea which suggests the distinct additional idea _C_. And
where the train of suggestion is one of reasoning distinctively
so-called as contrasted with mere 'revery,' ... the ideas bear
certain inward relations to each other which we must carefully
examine. The result _C_ yielded by a true act of reasoning
is apt to be a thing voluntarily _sought_, such as the means
to a proposed end, the ground for an observed effect, or the
effect of an assumed cause."[2] Thus what at first sight might
seem a fantastic suggestion may, when its bearings are logically
followed out, be seen in one of its aspects to be the key
to the solution of a problem. To primitive man it might have
seemed absurd to suggest that flowing water might be used
as power; to the man in Franklin's day that the same force
that was exhibited in the lightning might be used in transportation
and in lighting houses.[1]

[Footnote 1: James: _Psychology_, vol. II, p. 343.]

[Foo