ver our object. We
must not endeavor to change the principles of language, but to
understand and explain them; to ascertain, as far as possible, the
actions of the mind in obtaining ideas, and the use of language in
expressing them. We may not be able to make our sentiments understood;
but if they are not, the fault will originate in no obscurity in the
facts themselves, but in our inability either to understand them or the
words employed in their expression. Having been in the habit of using
words with either no meaning or a wrong one, it may be difficult to
comprehend the subject of which they treat. A man may have a quantity of
sulphur, charcoal, and nitre, but it is not until he learns their
properties and combinations that he can make gunpowder. Let us then
adopt a careful and independent course of reasoning, resolved to meddle
with nothing we do not understand, and to use no words until we know
their meaning.

A complex idea is a combination of several simple ones, as a tree is
made up of roots, a trunk, branches, twigs, and leaves. And these again
may be divided into the wood, the bark, the sap, &c. Or we may employ
the botanical terms, and enumerate its external and internal parts and
qualities; the whole anatomy and physiology, as well as variety and
history of trees of that species, and show its characteristic
distinctions; for the mind receives a different impression on looking at
a maple, a birch, a poplar, a tamarisk, a sycamore, or hemlock. In this
way complex ideas are formed, distinct in their parts, but blended in a
common whole; and, in conformity with the law regulating language,
words, sounds or signs, are employed to express the complex whole, or
each distinctive part. The same may be said of all things of like
character. But this idea I will illustrate more at large before the
close of this lecture.

First impressions are produced by a view of material things, as we have
already seen; and the notion of action is obtained from a knowledge of
the changes these things undergo. The idea of quality and definition is
produced by contrast and comparison. Children soon learn the difference
between a sweet apple and a sour one, a white rose and a red one, a hard
seat and a soft one, harmonious sounds and those that are discordant, a
pleasant smell and one that is disagreeable. As the mind advances, the
application is varied, and they speak of a sweet rose, changing from
_taste_ and _sight_ to smell, of a