t we are not thus conscious of our mental life. We can and do use
our mental states without being able to describe them accurately. In a
sense, we are conscious of what is there, but our consciousness is
rather dim and vague, and in our attempts to give an account of it we
are in no little danger of giving a false account.

Thus, the psychologist assumes that we perceive both physical phenomena
and mental--the external world and the mind. He takes it for granted
that we perceive mental phenomena to be related to physical. He is
hardly in a position to make this assumption, and then to set it aside
as a thing he need not further consider. Does he not tell us, as a
result of his investigations, that we can know the external world only
as it is reflected in our sensations, and thus seem to shut the mind up
within the circle of mental phenomena merely, cutting off absolutely a
direct knowledge of what is extra-mental? If we can know only mental
phenomena, the representatives of things, at first hand, how can we
tell that they are representatives? and what becomes of the assumption
that we _perceive_ that mind is related to an external world?

It may be said, this problem the psychologist may leave to the
metaphysician. Certainly, it is one of those problems that the
metaphysician discusses; it has been treated in Chapter IV. But my
contention is, that he who has given no thought to the matter may
easily fall into error as to the very nature of mental phenomena.

For example, when we approach or recede from a physical object we have
a series of experiences which are recognized as sensational. When we
imagine a tree or a house we are also experiencing a mental phenomenon.
All these experiences _seem_ plainly to have extension in some sense of
the word. We appear to perceive plainly part out of part. In so far,
these mental things seem to resemble the physical things which we
contrast with what is mental. Shall we say that, because these things
are mental and not physical, their apparent extension is a delusion?
Shall we say that they really have no parts? Such considerations have
impelled psychologists of eminence to maintain, in flat contradiction
to what seems to be the unequivocal testimony of direct introspection,
that the total content of consciousness at any moment must be looked
upon as an indivisible, part-less unit.

We cannot, then, depend merely on direct introspection. It is too
uncertain in its d