Speculations on Metaphysics

I--THE MIND

It is an axiom in mental philosophy, that we can think of nothing
which we have not perceived. When I say that we can think of nothing,
I mean, we can imagine nothing, we can reason of nothing, we can
remember nothing, we can foresee nothing. The most astonishing
combinations of poetry, the subtlest deductions of logic and
mathematics, are no other than combinations which the intellect
makes of sensations according to its own laws. A catalogue of all
the thoughts of the mind, and of all their possible modifications,
is a cyclopedic history of the universe.

But, it will be objected, the inhabitants of the various planets of
this and other solar systems; and the existence of a Power bearing
the same relation to all that we perceive and are, as what we
call a cause does to what we call effect, were never subjects of
sensation, and yet the laws of mind almost universally suggest,
according to the various disposition of each, a conjecture,
a persuasion, or a conviction of their existence. The reply is
simple; these thoughts are also to be included in the catalogue
of existence; they are modes in which thoughts are combined; the
objection only adds force to the conclusion, that beyond the limits
of perception and thought nothing can exist.

Thoughts, or ideas, or notions, call them what you will, differ
from each other, not in kind, but in force. It has commonly been
supposed that those distinct thoughts which affect a number of
persons, at regular intervals, during the passage of a multitude
of other thoughts, which are called REAL or EXTERNAL OBJECTS,
are totally different in kind from those which affect only a few
persons, and which recur at irregular intervals, and are usually
more obscure and indistinct, such as hallucinations, dreams, and the
ideas of madness. No essential distinction between any one of these
ideas, or any class of them, is founded on a correct observation of
the nature of things, but merely on a consideration of what thoughts
are most invariably subservient to the security and happiness of
life; and if nothing more were expressed by the distinction, the
philosopher might safely accommodate his language to that of the
vulgar. But they pretend to assert an essential difference, which
has no foundation in truth, and which suggests a narrow and false
conception of universal nature, the parent of the most fatal errors
in speculation. A specific difference between every thought of the
mind, is, indeed, a necessary consequence of that law by which it
perceives diversity and number; but a generic and essential difference
is wholly arbitrary. The principle of the agreement and similarity
of all thoughts, is, that they are all thoughts; the principle
of their