disease as
to be unfit for the formation and retention of the proper phantasms,
then your intellect either would not work at all or it would work
abnormally; your mind would then be insane.

4. Now, in an infant the brain is still too soft and imperfect to form
the proper phantasms from which the intellect is to elaborate its ideas.
A false school of psychology would say that the infant's brain cannot
yet _ideate_; but that is incorrect language. No brain can ideate or
form ideas; an idea is an intellectual or mind image, not a brain image;
it is an abstract and universal image, and matter cannot represent but
what is concrete and individual. Only a simple and spiritual being, the
rational soul, can form ideas. Nevertheless our soul, in its present
state of substantial union with our body, is extrinsically dependent on
the body; to form ideas it needs to have the sensible object presented
to it by a phantasm or brain-picture. Now, a child born blind and deaf,
and thus having its mind, as it were, cut off from communication with
the outer world, could scarcely form the necessary phantasms, because
the clogged senses could not supply proper materials for them; such a
child would, therefore, be apt to remain idiotic. And even in children
whose outer senses are sound the brain or the nervous system may be too
imperfect to allow of its forming proper phantasms. In this torpor of
the mind then consists the first kind of mental unsoundness, that of
_idiocy_, or its milder form _imbecility_. In old age, and in peculiar
diseases, the worn-out system may return to a second childhood, then
called _dementia_ or _dotage_. The existence of such species of insanity
is not difficult to discover.

5. The second and more common form of insanity, and that which it is
often difficult to discover and pronounce upon with certainty, is that
which I have called _delusional_ or _illusional_. Its characteristic
trait, its very essence, lies in this, that the insane man mistakes what
he imagines for what is real; and he cannot be made to distinguish
between imagination and reality, though the difference is obvious to an
intellect in its normal state.

In this connection, it is well to point out a distinction, not always
observed, but useful to explain the workings of an insane mind, between
_illusions_, _hallucinations_, and _delusions_.

(_a_) An _illusion_ is properly a deception arising from a mistake in
sense-perception; as when a half-dr