THE CLASSIFICATION OF ILLUSIONS.
If illusion is the simulation of immediate knowledge, the most obvious
mode of classifying illusions would appear to be according to the
variety of the knowledge which they simulate.
Now, the popular psychology that floats about in the ordinary forms of
language has long since distinguished certain kinds of unreasoned or
uninferred knowledge. Of these the two best known are perception and
memory. When I see an object before me, or when I recall an event in my
past experience, I am supposed to grasp a piece of knowledge directly,
to know something immediately, and not through the medium of something
else. Yet I know differently in the two cases. In the first I know by
what is called a presentative process, namely, that of sense-perception;
in the second I know by a representative process, namely, that of
reproduction, or on the evidence of memory. In the one case the object
of cognition is present to my perceptive faculties; in the other it is
recalled by the power of memory.
Scientific psychology tends, no doubt, to break down some of these
popular distinctions. Just as the zoologist sometimes groups together
varieties of animals which the unscientific eye would never think of
connecting, so the psychologist may analyze mental operations which
appear widely dissimilar to the popular mind, and reduce them to one
fundamental process. Thus recent psychology draws no sharp distinction
between perception and recollection. It finds in both very much the same
elements, though combined in a different way. Strictly speaking, indeed,
perception must be defined as a presentative-representative operation.
To the psychologist it comes to very much the same thing whether, for
example, on a visit to Switzerland, our minds are occupied in
_perceiving_ the distance of a mountain or in _remembering_ some
pleasant excursion which we made to it on a former visit. In both cases
there is a reinstatement of the past, a reproduction of earlier
experience, a process of adding to a present impression a product of
imagination--taking this word in its widest sense. In both cases the
same laws of reproduction or association are illustrated.
Just as a deep and exhaustive analysis of the intellectual operations
thus tends to identify their various forms as they are distinguished by
the popular mind, so a thorough investigation of the flaws in these
operations, that is to say, the counterfeits of knowledge, will probably
lead to an identification of the essential mental process which
underlies them. It is apparent, for example, that, whether a man
_projects_ some figment of his imagination into the external world,
giving it, present material reality, or whether (if I may be allowed the
term) he _retrojects_ it into the dim region of the past, and takes it
for a reality that has been he is committing substantially the same
blunder. The source of the illusion in both cases is one and the same.
It might seem to follow from this that a scientific discussion of the
subject would overlook the obvious distinction between illusions of
perception and those of memory; that it would attend simply to
differences in the mode of origination of the illusion, whatever its
external form. Our next step, then, would appear to be to determine
these differences in the mode of production.
That there are differences in the origin and source of illusion is a
fact which has been fully recognized by those writers who have made a
special study of sense-illusions. By these the term illusion is commonly
employed in a narrow, technical sense, and opposed to hallucination. An
illusion, it is said, must always have its starting-point in some actual
impression, whereas a hallucination has no such basis. Thus it is an
illusion when a man, under the action of terror, takes a stump of a
tree, whitened by the moon's rays, for a ghost. It is a hallucination
when an imaginative person so vividly pictures to himself the form of
some absent friend that, for the moment, he fancies himself actually
beholding him. Illusion is thus a partial displacement of external fact
by a fiction of the imagination, while hallucination is a total
displacement.
This distinction, which has been adopted by the majority of recent
alienists[1], is a valuable one, and must not be lost sight of here. It
would seem, from a psychological point of view, to be an important
circumstance in the genesis of a false perception whether the
intellectual process sets out from within or from without. And it will
be found, moreover, that this distinction may be applied to all the
varieties of error which I propose to consider. Thus, for example, it
will be seen further on that a false recollection may set out either
from the idea of some actual past occurrence or from a present product
of the imagination.
It is to be observed, however, that the line of separation between
illusion and hallucination, as thus defined, is a very narrow one. In by
far the largest number of hallucinations it is impossible to prove that
there is no modicum of external agency co-operating in the production of
the effect. It is presumable, indeed, that many, if not all,
hallucinations have such a basis of fact. Thus, the madman who projects
his internal thoughts outwards in the shape of external voices may, for
aught we know, be prompted to do so in part by faint impressions coming
from the ear, the result of those slight stimulations to which the organ
is always exposed, even in profound silence, and which in his case
assume an exaggerated intensity. And even if it is clearly made out that
there are hallucinations in the strict sense, that is to say, false
perceptions which are wholly due to internal causes, it must be conceded
that illusion shades off into hallucination by steps which it is
impossible for science to mark. In many cases it must be left an open
question whether the error is to be classed as an illusion or as a
hallucination.[2]
For these reasons, I think it best not to make the distinction between
illusion and hallucination the leading principle of my classification.
However important psychologically, it does not lend itself to this
purpose. The distinction must be kept in view and illustrated as far as
possible. Accordingly, while in general following popular usage and
employing the term illusion as the generic name, I shall, when
convenient, recognize the narrow and technical sense of the term as
answering to a species co-ordinate with hallucination.
Departing, then, from what might seem the ideally best order of
exposition, I propose, after all, to set out with the simple popular
scheme of faculties already referred to. Even if they are,
psychologically considered, identical operations, perception and memory
are in general sufficiently marked off by a speciality in the form of
the operation. Thus, while memory is the reproduction of something with
a special reference of consciousness to its past existence, perception
is the reproduction of something with a special reference to its present
existence as a part of the presented object. In other words, though
largely _representative_ when viewed as to its origin, perception is
_presentative_ in relation to the object which is supposed to be
immediately present to the mind at the moment.[3] Hence the convenience
of recognizing the popular classification, and of making it our
starting-point in the present case.
All knowledge which has any appearance of being directly reached,
immediate, or self-evident, that is to say, of not being inferred from
other knowledge, may be divided into four principal varieties: Internal
Perception or Introspection of the mind's own feelings;
External Perception; Memory; and Belief, in so far as it simulates the
form of direct knowledge. The first is illustrated in a man's
consciousness of a present feeling of pain or pleasure. The second and
the third kinds have already been spoken of, and are too familiar to
require illustration. It is only needful to remark here that, under
perception, or rather in close conjunction with it, I purpose dealing
with the knowledge of other's feelings, in so far as this assumes the
aspect of immediate knowledge. The term belief is here used to include
expectations and any other kinds of conviction that do not fall under
one of the other heads. An instance of a seemingly immediate belief
would be a prophetic prevision of a coming disaster, or a man's
unreasoned persuasion as to his own powers of performing a difficult
task.
It is, indeed, said by many thinkers that there are no legitimate
immediate beliefs; that all our expectations and other convictions about
things, in so far as they are sound, must repose on other genuinely
immediate knowledge, more particularly sense-perception and memory.
This difficult question need not be discussed here. It is allowed by all
that there is a multitude of beliefs which we hold tenaciously and on
which we are ready to act, which, to the mature mind, wear the
appearance of intuitive truths, owing their cogency to nothing beyond
themselves. A man's belief in his own merits, however it may have been
first obtained, is as immediately assured to him as his recognition of a
real object in the act of sense-perception. It may be added that many of
our every-day working beliefs about the world in which we live, though
presumably derived from memory and perception, tend to lose all traces
of their origin, and to simulate the aspect of intuitions. Thus the
proposition that logicians are in the habit of pressing on our
attention, that "Men are mortal," seems, on the face of it, to common
sense to be something very like a self-evident truth, not depending on
any particular facts of experience.
In calling these four forms of cognition immediate, I must not, however,
be supposed to be placing them on the same logical level. It is plain,
indeed, to a reflective mind that, though each may be called immediate
in this superficial sense, there are perceptible differences in the
degree of their immediacy. Thus it is manifest, after a moment's
reflection, that expectation, so far as it is just, is not primarily
immediate in the sense in which purely presentative knowledge is so,
since it can be shown to follow from something else. So a general
proposition, though through familiarity and innumerable illustrations it
has acquired a self-evident character, is seen with a very little
inspection to be less fundamentally and essentially so than the
proposition, "I am now feeling pain;" and it will be found that even
with respect to memory, when the remembered event is at all remote, the
process of cognition approximates to a mediate operation, namely, one of
inference. What the relative values of these different kinds of
immediate knowledge are is a point which will have to be touched on at
the end of our study. Here it must suffice to warn the reader against
the supposition that this value is assumed to be identical.
It might seem at a first glance to follow from this four-fold scheme of
immediate or quasi-immediate knowledge that there are four varieties of
illusion. And this is true in the sense that these four heads cover all
the main varieties of illusion. If there are only four varieties of
knowledge which can lay any claim to be considered immediate, it must be
that every illusion will simulate the form of one of these varieties,
and so be referable to the corresponding division.
But though there are conceivably these four species of illusion, it does
not follow that there are any actual instances of each class
forthcoming. This we cannot determine till we have investigated the
nature and origin of illusory error. For example, it might be found that
introspection, or the immediate inspection of our own feelings or mental
states, does not supply the conditions necessary to the production of
such error. And, indeed, it is probable that most persons, antecedently
to inquiry, would be disposed to say that to fall into error in the
observation of what is actually going on in our own minds is
impossible.
With the exception of this first division, however, this scheme may
easily be seen to answer to actual phenomena. That there are illusions
of perception is obvious, since it is to the errors of sense that the
term illusion has most frequently been confined. It is hardly less
evident that there are illusions of memory. The peculiar difficulty of
distinguishing between a past real event and a mere phantom of the
imagination, illustrated in the exclamation, "I either saw it or dreamt
it," sufficiently shows that memory is liable to be imposed on. Finally,
it is agreed on by all that the beliefs we are wont to regard as
self-evident are sometimes erroneous. When, for example, an imaginative
woman says she knows, by mere intuition, that something interesting is
going to happen, say the arrival of a favourite friend, she is plainly
running the risk of being self-deluded. So, too, a man's estimate of
himself, however valid for him, may turn out to be flagrantly false.
In the following discussion of the subject I shall depart from the above
order in so far as to set out with illusions of sense-perception. These
are well ascertained, forming, indeed, the best-marked variety. And the
explanation of these has been carried much further than that of the
others. Hence, according to the rule to proceed from the known to the
unknown, there will be an obvious convenience in examining these first
of all. After having done this, we shall be in a position to inquire
whether there is anything analogous in the region of introspection or
internal perception. Our study of the errors of sense-perception will,
moreover, prove the best preparation for an inquiry into the nature and
mode of production of the remaining two varieties.[4]
I would add that, in close connection with the first division, illusions
of perception, I shall treat the subtle and complicated phenomena of
dreams. Although containing elements which ought, according to
strictness, to be brought under one of the other heads, they are, as
their common appellation, "visions," shows, largely simulations of
external, and more especially visual, perception.
Dreams are no doubt sharply marked off from illusions of
sense-perception by a number of special circumstances. Indeed, it may be
thought that they cannot be adequately treated in a work that aims
primarily at investigating the illusions of normal life, and should
rather be left to those who make the pathological side of the subject
their special study. Yet it may, perhaps, be said that in a wide sense
dreams are a feature of normal life. And, however this be, they have
quite enough in common with other illusions of perception to justify us
in dealing with them in close connection with these.