Material objects are all either not living, that is to say, mineral
bodies, or they are living bodies. Everything which occupies space,
offers resistance, has weight and transfers motion, belongs to one or
other of these two great provinces of nature. The sciences of Astronomy,
Mineralogy, Physics, and Chemistry deal with the former, while Biology,
with its two divisions of Zoology and Botany, treats of the latter. But
natural knowledge is not exhausted by this catalogue of its topics. In
the very first paragraph of this Primer, in fact, we had occasion to
draw a distinction between =Things=, or material objects, and
=Sensations=; and a moment’s reflection is sufficient to convince you
that sensations are not material objects. A smell takes up no space and
has no weight; and to speak of a pound or of a cubic foot of sound, or
of brightness, is, on the face of the matter, an absurdity. Pleasure is
said metaphorically to be fugitive, but you cannot imagine a pleasure as
a thing in motion.
What we call our =Emotions= are in like manner devoid of all the
characters of material bodies. Love and hatred, for example, cannot for
a moment be conceived to have shape, or weight, or momentum. And when,
in reasoning, we think, our =Thoughts= have the same lack of the
qualities of material things.
Sensations, emotions, and thoughts, thus constitute a peculiar group of
natural phenomena, which are termed =mental=.