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 ...

4-18 REASONING AND DEDUCTIVE EVIDENCE.
employment to the samne faculties of the mind. The poet, the
painter, the gardener, and the botanist, are all occupied, in various degrees and modes, with the study of the vegetable kingdom; yet who has ever thought of confounding their several
pursuits under one common name? The natural historian, the
civil historian, the moralist, the logician, the dramatist, and the
statesman, are all engaged in the study of man, and of the principles of human nature; yet how widely discriminated are these
various departments of science and of art! how different are
the kinds of evidence on which they respectively rest! how
different the intellectual habits which they have a tendency to
form! Indeed, if this mode of generalization were to be admitted as legitimate, it would lead us to blend all the objects of
science into one and the same mass; inasmuch as it is by the
same impressions on our external senses, that our intellectual
faculties are, in the first instance, roused to action, and all the
first elements of our knowledge unfolded.
In the instance, however, before us, there is a very remarkable
specialty, or rather singularity, which renders the attempt to identify the objects of geometrical and physical science inconmparably more illogical than it would be to classify poetry with botany,
or the natural history of man with the political history of nations.
This specialty arises from certain peculiarities in the metaphysical nature of those sensible qualities which fall under the consideration of the geometer; and which led me, in a different work, to
distinguish them from other sensible qualities (both primary and
secondary,) by bestowing on them the title of mathematical cifections of matter. Of these mathematical affections (magnitude
and figure) our first notions are, no doubt, derived (as well as of
hardness, softness, roughness, and smoothness) from the exercise
of our external senses; but it is equally certain, that when the
notions of magnitude and figure have once been acquired, the
mind is immediately led to consider them as attributes of space
no less than of body: and (abstracting them entirely firom the
other sensible qualities perceived in conjunction with them-)
becomes impressed with an irresistible conviction, that their
existence is necessary and eternal, and that it would remain un