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complicated, but the mental state felt to be simple
must be described by the psychologist as such.^

Somewhat similarly, in the case of touch, a
certain interval of space, variable in different
portions of the body, must exist between the parts
of the organism affected by two stimuli, m order
that these may be felt as distinct. The capacity of
sensation for variation in intensity and duration has
suggested in recent times the attempt to secure
exact quantitative measurement of mental pheno-
mena, and the title of Psycho physics has been
allotted to this line of investigation.

Cognitive character of Sensation — The features
hitherto described, including even pleasantness or
painfulness, are merely aspects or accidental pro-
perties of sensation. Its essential nature lies in its
cognitive quality. The intensity, duration, and
emotional tone of a sensation, exist only as they are
known. They are of a variable and adjectival
nature. They determine and modify, but they do

2 The "objective " analysis of mental states by Mr Spencer and
M.Taine is thus illusory. If states which consciousness— the only
possible witness concerning such facts — declares to be simple, are
to be reduced to units of the character of nervous shocks, because
the action of the physical agent is of a composite character, then we
certainly cannot stop at the feeling of a " shock," as the unit. The
briefest and simplest sensation of the colour of violet, which involves
between six and seven hundred billions of vibrations in the second,
must be resolved into an incredible number of unconscious units of
consciousness, for the existence of none of which, of course, is there
any evidence A knowledge of the physical conditions of mental
states is valuable, but conscious elements affirmed to be simple by
introspection, must be accepted as such by the psychologist.
"Mental facts," as Mr. Mark Baldwin urges, "are simple states,
and they are nothing independently of the mind whose states they are."
(Cf. Senses and Intellect, pp. gS— io6; also Dr. Mivart, Nature and
Thought, 2nd Edit., pp. 89—92.) See also pp. 510—512, below.

SENSATI0>^. 4q

not constitute the essence of a sensation. A sensa-
tion is in itself an elementary mode of consciousness
of a cognitional character. Knowledge, however,
may have reference either to extra-organic, or to
intra- organic objects and events. We may be
cognizant of something other than ourselves, or of
the states of our own sentient organism, and different
censes stand higher and lower in regard to these
different fields. In sight, in the muscular sense,^
and in the tactual sensations of pressure, knowledge
of external reality is the prominent feature ; in
hearing, taste, smell, and the organic feelings, the
sensation is a cognition, which originally bore a
subjective character. In the case of these latter
faculties, the pleasurable or painful aspects of sensa-
tions frequently rise to great importance ; and on
some occasions the sensation becomes mainly a
cognition of pain, or, more rarel}^ of pleasure.

Sensation and Perception. — Tiiis distinction between the
objective and subjective import of the sentient act has caused
the two terms, sensation and perception, to be contrasted witli
each other. Sensation, as thus opposed to perception, is
variously defined to be, tlie modification of the sense viewed
merely as a subjective state, the consciousness of an affection
of the organism, or the feeling of pleasure or pain awakened
by the stimulus. Perception^ is described as the objective

" This term is used to denote the power of experiencing sensa-
tions of resistance or impeded energy and movement. Its nature
will be discussed in the next chapter.

^ The word perception, or rather, the Latin verb percipere, was
originally used in a wide sense to denote any form of apprehension
or comprehension, whether sensuous or intellectual. Later on. it
became limited to sensuous apprehension, and was employed by
Reid, in contrast to the term sensation, to designate the sensuous
cognition of something as external to us. Sensation originally meant
the process of sensuous apprehension considered as revealing to us
both itself as a subjective state, and the objective quality to which
it corresponded. By Reid it was confined to the former significa-


knowledge, the apprehension of external reality given in the
sentient act ; or, as the act by which we locahze or project a
sensation or cluster of sensations, actual and possible, into
the external world. .

This separation of the two terms is convenient for bring-
ing out the difference between the developed form of cognition
exhibited by sense in mature life, and the vague kind of
apprehension afforded in the earlier acts of the sentient
powers : but the distinction is one of degree, not of kind. In
the most rudimentary sensations of pressure and of colour,
there is a cognition of something other than self, and though
rude and indefinite in character, this is still an act of objective
kTiowledge. Consequently, there is already here perception,
in the modern signification of the term. This vague act
receives exacter definition as we advance, and in later years
the quality perceived by the sense is cognized as situated in
a determinate place, and accompanied by other qualities.
Such further determinations, are, however, the result of other
sensations, and if no one of them revealed external reality to
us, the aggregate could not do so. This subject will be better
understood when we come to treat of the nature of Perception.
Some writers define Sensation as the feeling of pleasure or
pain attached to an act of sensuous apprehension, but very
few, if any, adhere consistently to this interpretation. When,
for instance, the sensations of the different senses are spoken
of, and their various properties, quality, intensity, tone, dura-
tion, and the rest, are described by psychologists, sensation
does not mean the pleasurable or painful aspect of certain
mental states, but these states themselves. It is only when
used in this narrow signification, as a feeling of pleasure or
pain, that sensation and perception can be held within certain
limits to stand in an inverse relation to each other.^

tion.and thus explained : "The agreeable odour (of a rose) which,
I feel, considered by itself without relation to any external object,
is merely a sensation. Perception has always an external object,
and the object in this case is that quality in the rose which I discern
by the sense of smell." The later sensationalists {e.s;;. Mr. Sully,
Outlines, c. vi.), inverting the doctrine of Reid and Hamilton, that
perception is the apprehension of a real external quality, describe
this act as an ejection or projection out of the mind of a sensation
carrying with it a cluster of faint representations of other past
sensations, the whole being "solidified" or "integrated" in the
form of an object. On the terms sensation and perception,
cf. Hamilton, On Reid, Note D, also Metapli. Vol. H. 93—97.

5 Hamilton explains Reid to mean by perception. " the objective
knowledge we have of an external reality through the senses ; by
sensation, the subjective feeling of pleasure or pain with which the


The modification of a sensuous faculty is thus,
in its simplest form, of a percipient character, and
in the case of vision and touch, the sensation from
the beginning possesses a certain objective refer-
ence. A sensation viewed in this way as a modifi-
cation by which the mind is made cognizant of a
material quality of an object, was called by the
schoolmen a species sensibilis.

The Scholastic Doctrine of Species.— The doctrine of
species has been attacked and ridiculed by man}- modern
writers, and this in a manner which sfiows how widespread
and profound, even amongst students of philosophy, is the
ignorance regarding the most familiar terms of scholastic
writers. Democritus and Epicurus formerly taught that we
know objects by means of minute representative images which
stream off from their surface, and pass into our soul through
the channels of the senses. The Latin word species, meaning
an image, was used by their Roman disciples to signify these
volatile images. Aristotle and his followers, however, rejected
the theory of a physical efflux of species, and taught instead,
that objects effected modifications in the mind by acting on
the sense-organs through motions in the intervening media.
The term species was later on employed to denote these modi-
fications by which the mind is made to apprehend the exterior
object. In this sense, which is that accepted by the greatest
philosophers of the middle ages, such as St. Thomas, Albertus

organic operation of sense is accompanied," and adopting this view
he enunciated the law that above a certain point the stronger the sensa-
tion the iveakcr the perception, and vice versa. He seeks to establish
this general opposition by a comparison (a) of the several senses,
and {b) of different impressions within the same sense. Confined to
sensuous apprehension, the formula seems to be approximately true,
although it is pain rather than pleasure which interferes with
cognition. As a generalization applicable to higher intellectual
forms of cognitive activity, it does not hold. Consciousness is not,
as Hamilton seems to imply, a fi.xed quantity where increase in
cognition involves decrease in feeling. This is in direct opposition
to the doctrine adopted by Hamilton himself from Aristotle, that
pleasure is a reflex of mental energy. In the view of the Greek
philosopher, keen and intense pleasure accompanies vigorous
intellectual activity, and the greatest and best pleasure is the
necessary sequela of the exercise of the highest form of cognitive
energy. (Cf. Hamilton, Metaph. pp. 93 — 105.)


Magnus, and Scotus, the species is not an entity which ha&
immigrated into the mind from the object, but a modification
or disposition awakened in the mind by the action of the
object. They teach, moreover, that this mental modification
is not what is primarily perceived in the act of simple appre-
hension. The mind, they hold, directly tends towards the
objective reality; and only by a reflex or concomitant act does
it cognize the mental state as such. With them. Species non
est id quod primo percipihir, sed id quo res percipitur. It is the
medium vel principium quo, non ex quo, res cognoscitnr. In other
words, the species is not an intermediate representation from
which the mind infers the object, but a psychical modification
by which the mind is lii^ened, or conformed, to the object, and
thus determined to cognize it.°

Intentionalis. — The adjective intentionalis was added to the
term species to signify that the cognition, though truly reflecting
the external object, does not resemble it in nature. The
mental modification was held to be merely a psychical or
spiritual expression of the material thing. Resemblance is of
many kinds. A photograph, or a statue, is, in a certain sense,
utteily unlike a man formed of flesh and blood; the blind

^ If the primary object of cognition were the mind's own unex-
tended modification, idealism and relativism would be inevitable.
" Qnidam posuerunt, quod vires, quae sunt in nobis cognoscitivae
nih 1 cognoscunt, msx proprias passiones, puta, quod sensus non sentit
nisi passionem sui organi, et secundum hoc intellectus nihil intel-
ligit, nisi suam passionem, scilicet speciem intelligibilem in se
receptam ; et secundum hoc species hujusmodi est ipsum quod intelli-
gitur. Sed haec opinio manifeste apparet falsa ex duobus. Primo
quidem, quia eadem sunt quae intelligimus, et de quibus sunt
scientiae ; si igitur ea, quoe intelligimus essent solum species quae
sunt in anima, sequeretur quod scientiae omnes non essent de rebus,
quae sunt, extra animam, sed solum de speciebus inttlligibilibus quae
sunt in anima. Secundo, quia sequeretur error antiquoruni dicentium,
omne quod videtur, esse verum ; et similiter quod contradictoriae
essent simul verae ; si enim potentia non cognoscit ni^i propriam
passionem, de ea solum judicat . . . puta si gustus non sentit nisi
propriam passionem, cum aliquis habens sanum gustum judicat mel
esse dulce, vere judicabit; et similiter si ille, qui habet gustum
infectum, judicet mel esse amarum vere judicabit ; uterque enim
judicabit secundum quod gustus ejus aflicitur. . . . Et ideo dicen-
dum est quod species intelligibilis se habet ad intellectum ut quo
intelli£;it intellectus. . . .

" Sed quia intellectus supra seipsum reflectitur, secundum
eandem reflexionem intelligit et suum intelligere et speciem qua
intelligit. Et sic species intellecta sccundario est id quod intelligitur.
Sed / J ^7/oi intelligitur /n/«c) est res cujus species intelligibilis est
simiUtudo." {Sum. la. q. 85. a. 2.)


man's representation of a circle by the sense of touch, is very
different from the visual image of the same figure ; the intel-
lectual ideas aroused by the words, "equality," "colour,'^
"square," must be widely divergent from both the image and
the reality to which they correspond. Yet, in spite of these
unlikenesses, there exist genuine relations of similarity
between such pairs of things as those just mentioned. The
scholastic writers adopting this view, taught that our know-
ledge, although in itself, as a mental activity, opposed in
nature to material reality, docs, nevertheless, truly inirror the
surrounding world. They held that though neither the tactual
nor the visual image resembles in nature the brass circular
substance presented to the sense, yet both accurately reflect
and are truly like the external reality ; and they called these
mental expressions of the object species intcntioiuilcs.

Species sensibiles et intelligibiles. — Furthermore, as the
schoolmen held the human mind to be capable of two
essentially distinct kinds of cognition, sensuous and intellec-
tual, they termed the apprehensive acts of the former species
sensibiles, of the latter species intelligibiles vel intellcctuales. In \
the genesis of the species they distinguished two moments ci 1
stages. The modification of the sensuous faculty, viewed as 1
an impression wrought in the mind by the action of the
object, was named the species impvessa. The reaction of the
mind as an act of cognitive consciousness was styled
the species expressa. The latter term designated the sensation
considered as a completed and perfect act of consciousness
elicited by the soul ; the former indicated the earlier stage of .
the process, the alteration in the condition of the mind looked \
at as an effect of the action of the object." The species proper, ^
however, whether impvessa or expressa, was an affection of the
mind. The term species corporal is was sometimes used to
signify the physical impression or movement produced by the
object in the organism, but the strict meaning of the word
species, and the only meaning of the term species intentionalis,
was the mental state. Thus, neither the image of the object
depicted on the retina of the eye, nor the nervous disturb-
ance propagated thence to the brain, but the conscious act
finally awakened, was held to be the true species or species

True doctrine. — Rejecting the interpretation of the species
as roving images, and every theory conceiving them as repre-
sentations mediating between the object and the cognitive

"^ The existence of the species impvessa ]" proved by the fact of
memory. That the alteration or modification wrought in the soul by
the act of perception must persist in some form, is established by
the facility of representation and recognition



faculty, the thought embodied in the doctrine is thoroughly
sound. Unless we are prepared to maintain that our soul
is born with all its future knowledge ready made, and wrapped
up in innate ideas, we must allow that the physical world
does somehow or ether act on our faculties, and that our
perceptions are due to the influence of material objects upon
us. The mind does not determine all its own modifications,
and the strongest volition is unable to make the deaf man
hear a word, or the blind man see a colour. But this is to
admit that the faculty is stirred into conscious life and
informed by dispositions wrought in it by the perceived object.
Further, unless we are ready to adopt the position of absolute
scepticism, we must hold that knowledge does somehow
correspond to reality. There is not a merely arbitrary con-
nexion between the object and its apprehension. The latter
is a true, though psychical expression of the former. This
subject will be more fully dealt with hereafter, but we have
said enough to justify the doctrine of species iutentionales, as
understood by St. Thomas, and the leading philosophers of
the school.^ The modern writer may prefer to describe the
perception of a triangle as a modification of the mind
mirroring or reflecting in terms of consciousness the external
object, but this is only the old doctrine in other phraseology.

Experimental Psychology. Psycho-physics.—

The ineasuremcnt of mental states. — If one ounce be added
to a weight of three ounces placed on our hand resting
upon the table, \ve can just distinguish the new sensa-
tion from the old. A single voice also makes a per-
ceptible increase in the sound when added to a musical
trio. If, however, we add a single unit to a weight of
thirty ounces or to a chorus of twenty voices, no
difference can be felt. By observing and comparing
sensations produced by stimuli varying in intensit}', a
German physiologist, Weber (1834), showed that the
incvemcnt necessary to he added to a given stimulus in order to
awaken a sensation consciously distinguishable from the former

^ Kven Hamilton confounds the maintenance of species with the
doctrine of mediate perception, and so looks on St. Thomas and the
great body of the schoolmen as representationalists or hypothetical
realists. (Cf On Reid, Note M, pp. 852 — 857.) The passage cited
from St. Thomas, p. 52, refutes the charge. For a full treatment of
the subject, see Sanseverino,D)';/

Online LibraryMichael MaherPsychology: empirical and rational → online text (page 6 of 63)