Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

144 ABSTRACTION.
exercise of their intellectual powers, two classes, whose habits
of thought are remarkably distinguished from each other; the
one class comprehending what we commlonly call men of business, or, more properly, men of detail; the other, men of abstraction; or, in other words, philosophers.
The advantages which, in certain respects, the latter of these
possess over the former, have been already pointed out; but it
must not be supposed, that these advantages are always purchased without some inconvenience. As the solidity of our
general principles depends on the accuracy of the particular
observations into which they are ultimately resolvable, so their
utility is to be estimated by the practical applications of which
they admit; and it unfortunately happens, that the same turn of
mind which is favorable to philosophical pursuits, unless it be
kept under proper regulation, is extremely apt to disqualify us
for applying our knowledge to use, in the exercise of the arts and
in the conduct of affairs.
"the danger of applying abstract principles incautiously. - In
order to perceive the truth of these remarks, it is almost sufficient to recollect, that as classifications, and, of consequence,
general reasoning, presupposes the exercise of abstraction; a
natural disposition to indulge in them, cannot fail to lead the
mind to overlook the speci'fic differences of things, in attending
to their common qualities. To succeed, however, in practice, a
familiar and circumstantial acquaintance with the particular
objects which fall under our observation, is indispensably necessary.
But further: As all general principles are founded on classifications which imply the exercise of abstraction, it is necessary to regard them, in their practical applications, merely as
approximations to the truth; the defects of which must be supplied by habits acquired by personal experience. In considering, for example, the theory of the mechanical powers; it is
usual to simplify the objects of our conception, by abstracting
from friction, and from the weight of the different parts of
which they are composed. Levers are considered as mathemnatical lines, perfectly inflexible; and ropes, as mathematical