science has not been satisfactorily constructed.

We are forced to admit that the science of psychology has not yet
emerged from the state in which a critical examination of its
foundations is necessary, and that the construction of the beaten path
is still in progress. This I shall try to make clear by illustrations.

The psychologist studies the mind, and his ultimate appeal must be to
introspection, to a direct observation of mental phenomena, and of
their relations to external things. Now, if the observation of mental
phenomena were a simple and an easy thing; if the mere fact that we are
conscious of sensations and ideas implied that we are _clearly_
conscious of them and are in a position to describe them with accuracy,
psychology would be a much more satisfactory science than it is.

But 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