roughly summarize these operations by saying that they
consist in the control of the lower automatic processes (association or
suggestion) by the higher activities of conscious will. This activity of
will takes the form now of an effort of attention to what is directly
present to the mind (sense-impression, internal feeling, mnemonic image,
etc.), now of conscious reflection, judgment, and reasoning, by which
the error is brought into relation to our experience as a whole,
individual and collective.

It is for the philosopher to investigate the inmost nature of these
operations as they exhibit themselves in our every-day individual
experience, and in the large intellectual movements of history. In no
better way can he arrive at what common sense and science regard as
certain cognition, at the kinds of knowledge on which they are wont to
rely most unhesitatingly.

There is one other relation of our subject to philosophic problems which
I have purposely left for final consideration. Our study has consisted
mainly in the psychological analysis of illusions supposed to be known
or capable of being known as such. Now, the modern association school
professes to be able to resolve some of the so-called intuitions of
common sense into elements exactly similar to those into which we have
here been resolving what are acknowledged by all as illusions. This fact
would seem to point to a close connection between the scientific study
of illusion and the particular view of these fundamental intuitions
taken by one philosophic school. In order to see whether there is really
this connection, we must reflect a little further on the nature of the
method which we have been pursuing.

I have already had occasion to rise the expression "scientific
psychology," or psychology as a positive science, and the meaning of
this expression must now be more carefully considered. As a positive
science, psychology is limited to the function of analyzing mental
states, and of tracing their origin in previous and more simple mental
states. It has, strictly speaking, nothing to do with the question of
the legitimacy or validity of any mental act.

Take a percept, for example. Psychology can trace its parentage in
sensation, the mode in which it has come by its contents in the laws of
association. But by common consent, a percept implies a presentative
apprehension of an object now present to sense. Is this valid or
illusory? This question psychology,