SUPPOSITIONS OF SCIENTIFIC THEORIES. PHYSICAL REALISM.

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We have seen (121, 123) that while the primary qualities are no

less relative to the perceiver than the secondary, it is impossible

to regard either class of qualities as mere states of consciousness,

mere phases or modes of the individual perceiving mind. Now

some have thought to find a via media between the idealist posi

tion on the one hand, and that of intuitive or perceptionist realism

on the other, by defending the view that the sense qualities are

neither conscious states nor modes of the external universe, but

diximus, nempe : Nece=se est ut ideale et recile ad unum principium revocentur,

quod utrumque explicet et utriusque sit ultima ratio. Hoc principium repeto esse

verissimum, imo fundamentum, quo tola nititur, quo tola niti debet philosophia;

quia necesse omnino est ut reale (natura finita) praecedatur ab ideali ; ideale autem

non potest ultimatim esse nisi in intellectu improducto, per se existente et aeterno,

qui solus sit realitas praecedens meram idealitatem, atque ideo non solum cognoscat

sed efficiat intelligibile ipsum scu ideale."

PHYSICAL REALISM 125

modes or states of the perceivers organism.^ This theory is

known as Physical Realism. Owing to its unquestioning accept

ance of external reality as conceived and interpreted by scientists

in modern physical theories, it is favoured by many scientists who,

while rejecting intuitive realism, do not care to commit them

selves to idealism. As a peculiar form of representationism it

deserves attention both for its application of the principle of

" inference by similarity," and for the opportunity it offers of

examining the presuppositions and assumptions common to itself

and to the current conceptions and theories of Physical Science.

Its line of reasoning is somewhat like this : Science, which is

"knowledge at its best," 2 assures us of the real nature of external

qualities or objects. Since nothing external can be immediately

apprehended, but only inferred (by the principle of similarity)

from data that are internal, we can ascertain the real nature of

these latter data only by asking ourselves from what kind of

data can we have inferred the objects which science assures us to

be externally real. Such data must, on the one hand, be internal

(for the internal alone can be immediately apprehended) ; but they

must, on the other hand, be physical, i.e. of the same order as

the objects inferred by science and indicated by it as externally

real : they cannot be merely psychic states, for psychic states

could not be like external physical objects. Therefore the data

in question must be really states of the perceiver s brain, nervous

system, and sense organs. But the only objects which science

assures us to be externally real are the (inferentially perceptible)

extension, volume, shape, motion, etc., which are like their in

ternal sensible correlates, and such transcendentally inferred

imperceptible modes of the former as e.g. corpuscles, undulations

of aether, etc. : 3 which imperceptible modes correspond externally

to the internal secondary qualities. And the reason why the

former externals are like their internal correlates, and the latter

unlike theirs, must be because the perceiver s sense organon is so

constituted that it is capable of assuming in itself, and presenting

to consciousness, states similar to the primary externals under

1 " For example, the hot felt and the white seen are produced by external objects

and are apprehended by internal sensations of touch and vision, but are themselves

respectively the tactile and the optic nerves sensibly affected in the manner appre

hended as hot and white." CASE, Physical Realism (London, Longmans, 1888), p.

25. " The hot felt is the tactile nerves heated, the white seen is the optic nerves

so coloured." Ibid., p. 24.

2 Op. cit., p. 37. 3 /M<*., pp.34-5.

126 THEOR Y OF KNO W LEDGE

the influence of the latter, whereas it can assume and present to

consciousness under the influence of the secondary externals only

states dissimilar to these. 1

Unfortunately, however, for this theory, there are no really

sufficient grounds for holding that the external causes of the in

ternal organic states called " primary qualities " are like these

qualities, while the external causes of the internal organic states

called " secondary qualities " are not like these latter : that " for

instance, external motion is like sensible motion, but external

heat is an imperceptible mode of motion while sensible heat is

not sensibly a motion at all ".-

For if the immediate datum or object of sense a\vareness is

always only an internal organic condition of the perceiver s

own sense organon (i.e. the sensorium or external sense organ,

the brain, and the nervous system), and if what is external is

known only by being inferred from this, then when we see a

moving train or feel a shower of hailstones the only reason we

have for inferring that the real " external motion " of the train

or of the hailstones is like the " sensible motion," i.e. the motion

which is the direct object of our awareness and which on this

theory is always a nerve motion (though it appears to conscious

ness certainly not as a nerve motion but as a train or hailstone

motion), is the reason contained in the principle that the effect

must resemble its cause. In other words, the inferred external

cause must resemble the internal, sensible appearance which is

its effect. But the internal, sensible appearance is an immediately

apprehended nerve motion or organic condition appearing as an

external train or hailstone motion. Therefore the real external

train or hailstone motion must resemble the internally apparent

train or hailstone motion which is really the nerve motion or

organic condition immediately apprehended.

But whatever force there is in this presentation of the matter,

it applies equally to the secondary qualities such as heat. Ac

cording to the theory, " sensible heat is not sensibly a motion at

all " : that is, what we are immediately aware of in perceiving

heat, and what is therefore an organic condition of our own

nerves, is a conscious datum in no way resembling the conscious

datum which is present in e.g. our vision of a moving train or

our tactual perception of the moving razor in shaving : the im

mediate data of our awareness in these two cases being likewise

1 Op. cit., pp. 23, 26. -Ibid., p. 26.

PHYSICAL REALISM 127

organic conditions of our own nerves. But if we infer from these

latter organic conditions (about the real nature of which scientists

know comparatively little ; but about which we all know that

they reveal, or appear as, train motions and razor motions re

spectively), that their external causes are real motions similar

to the internal appearances assumed by the organic conditions

themselves, surely we can and must infer from the consciously

different organic condition which is " sensible heat " that its ex

ternal cause and counterpart, viz. " external heat " as a quality of

the external world, is something different from the "external

motion" which is the supposed cause of the "sensible motion,"

rather than that " external heat is an imperceptible mode of [ex

ternal] motion ".

The author s reason for the latter inference is " because, though

at first sight sensible heat would demand a similar external ob

ject, when all the facts of sensible heat are accumulated they are

found to be the kind of facts that are only produced by motion"}-

So " sensible heat," which is admitted to be " not sensibly a

motion at all," can be shown by "corpuscular science" 2 to be

producible only by the influence exerted on our organism by an

insensible mode of insensible external motion, 3 i.e. by a some

thing about the nature and modes of which we can know only

what we infer, by the law of similarity, from " sensible motion,"

which sensible motion, whatever it really be, 4 is admittedly wholly

unlike " sensible heat " ? But no Science, corpuscular or otherwise,

has achieved any such feat:

Nor is the reason alleged for the contention (attributed to

Science 6 ) that "external, insensible objects" resemble internal

sensible objects in "primary qualities" but not in "secondary

qualities," and that, " as they are in external nature," 7 the latter

are " insensible modes " 8 of the former, as sound as it is plaus

ible. It runs as follows : 9 The "sensible effect," i.e. that of which

we are directly aware in perception, is the result of two causes,

the "external world " and the "nervous system," the latter re

ceiving the influence of the former " according to its suscepti

bility": a principle which we have already recognized (121);

1 Op. cit., p. 26, italics ours.

2 C/. ibid., p. 23. 3 Ibid., pp. 23, 31-2.

4 On the author s hypothesis it is really an internal nerve motion, appearing as

an external spatial motion of bodies.

B C/. supra, 112. G Ibid., p. 23. " Ibid.

8 Ibid. Ibid., p. 30.

1 2 8 THE OR Y OF NO WLEDGE

though we should say rather that the whole external perception

process is the result of two causes, (a) the external world, and (li)

the complex self-cause, at once conscious and organic. But mark

the author s application of the principle, Quidquid recipitur, ad

modum recipientis recipitur : "The nervous system is far more

susceptible of similar effects from primary than from secondary

qualities. It is more capable of reflecting the waves of the sea

than the undulations of the aether." l Hence " sense sometimes

presents motion as motion, but cannot help presenting the hot,

the red, etc., as heterogeneous to motion, because of the structure

of the sensory nerves ; [but] science, by comparing sensible

motion with the sensible facts of the hot, the red, etc., infers that

the external cause of the latter is really a mode of motion ". 2

Now this claim on behalf of Science, to have established a similarity

of external primary qualities to their supposed internal sense

correlates, and a dissimilarity of external secondary qualities to

theirs, is no better than a petitio principii. For Science must

start from what we are directly aware of. ;i If, therefore, what

we are directly aware of when perceiving " the waves of the sea "

be a physical motion or condition of our nervous system, and if

science assumes the right of inferring that because this sensible,

nervous motion or condition appears as motion of " the waves of

the sea," therefore the real and external (and, on this theory, " in

sensible " though " inferentially perceptible ") motion of " the

waves of the sea " is like the appearance assumed by the nervous

motion or condition, how can it consistently refuse to infer that

the real, external, " insensible " correlate of the internal, " sen

sible " nerve motion or condition which appears as heat is also

like this latter appearance ? As a matter of fact there is no

ground for supposing that the perceiver s nervous system (in

Physical Realising, or the perceiver s mind or consciousness (in

ordinary Representationist Realistii), "mirrors" or "reflects" or

" represents " the inferred external qualities of the external

1 Op. cit., p. 30. The " knowledge " which we have of the nervous system is

of the same order as the knowledge we have of extra-organic matter : its validity,

therefore, is part of the general problem.

Ibid., p. 31.

3 And Epistemology likewise : not from what scientists conclude to be externally

real (the " physical objects of science," or " present objects of scientific knowledge "-

CASE, op. cit., p. 36), nor from the forgotten and unknown " original data of sense "

in childnood (ibid., pp. 25, 35, 36), which is not the only alternati\-e, but from the

"sensible data" and all other conscious data (10) of mature life. Cf. infra,

pp. 132, 137.

PHYSICAL REALISM 129

universe more similarly, 1 so to speak, when these are primary

or " quantitative " qualities (extension, shape, motion, unity,

multitude, etc.) than when they are secondary qualities (heat,

colour, taste, smell, and tactile qualities).

Physical Realism, therefore, though commendable for its

assertion, as against Idealism, that the direct objects of our sense

awareness are physical realities and not ideas or psychic states,

nevertheless labours under very serious defects, some of which

are needless concessions to Idealism, while others are peculiar

to itself.

The obvious truth that whatever is known in any way, whether

sensuously or intellectually, must be consciously or cognitively

(" intentionaliter ") present to, or one and continuous with, the

knower, it interprets as implying not indeed that the direct and

immediate object of awareness must be an idea or psychic state

of the knower, but that it must be really internal to and really

, one with the knower : that therefore in perception it must be an

organic condition of the perceiver, since nothing " external " can

be "immediately perceived". 2 But it is neither self-evident

that nothing external can be immediately perceived, nor can we

admit the assertion that "scientific analysis" has proved the im

mediate perception of the external to be impossible. 3 If external

reality, by acting on the perceiver s sense organs, can efficiently

influence the conscious, perceptive mind or principle which

animates those sense organs, to elicit a consciously perceptive

act, we see no reason for denying that the external cause or

stimulus can be also the directly apprehended term of this

perceptive act.

Of course if the efficient causal influence of the external

factor be conceived, or rather imagined, as being productive only

of internal organic or nerve qualities which are imperceptible

modes of motion in the perceiver s material organism, then in

deed direct conscious or cognitive continuity of the external

factor with the perceiver s consciousness would be impossible.

But in the first place such a narrow and one-sided conception of

the nature and scope of efficient causal influence is unwarranted

and erroneous. 1 And in the second place, even if accepted, it

would not in the least enable us to see why or how we become

1 That we should rather expect the reverse has not escaped the notice of Idealists.

Cf. infra, 125.

*Ibid., p. 28. 3 Ibid. 4 Cf. Ontology, 104, pp. 392-6.

VOL. II. 9

1 30 THEOR Y OF KNO WLE D GE

consciously aware of our internal nerve conditions or qualities as

taste, smell, heat, colour, tactual texture or resistance ; or as ex

tension, volume, magnitude, shape, motion, spatial discontinuity,

or number.

This, therefore, is another defect in physical realism. The

perceiver s organism is material. The effects supposed to be

wrought in it by the action of the external world must therefore

be on this theory the same as the effects wrought on external

bodies themselves by their own interaction, viz. primary qualities

(supposed to be all reducible to modes of motion of a virtually

or formally extended, atomic or discontinuous, or spatially con

tinuous, matter or aether substrate), and secondary qualities

(supposed to be varieties of this motion), in the internal and

organic, no less than in the external and extra-organic, domain.

It does not in the least explain how we come to know any

qualities of the external material universe to say that we become

directly aware of what must be really the same classes of quali

ties in the internal material universe which is our own material

organism, and infer the former from the latter. For the latter

qualities, though subjective or internal in the sense of being

qualities of our organism, are still physical or extramental, or

beyond and independent of consciousness. 1 To say that we

immediately apprehend one (extramental) nerve state or condition

as hot, another as red, another as bitter, another as surface

extension, another as solidity or volume or shape, another as

motion, and so on, is to make an ultimate assertion of something

just as mysterious and incapable of further analysis, and certainly

no more credible, than the assertion that what we immediately

apprehend in those various ways are states, conditions, or qualities

of the external material universe itself.

If the concretely qualified data or objects of which we become

directly aware in normal external sense perception are not

really external, as they are spontaneously judged to be, if they

are really internal (whether psychic and intramental, or organic

and physical and extramental), and if " everything external is

inferred " - from such internal (psychic or organic, immediately

1 The idealist escapes this difficulty by holding that no sense qualities are

physical, that all are purely mental or psychic. The supporter of ordinary repre-

sentationist realism escapes it by holding that the internal effects from which he

infers the external qualities are not merely organic, but are psychic, mental,

conscious impressions or representations.

2 Op. cit., p. zS.

PHYSICAL REALISM 131

apprehended objects of awareness), then there is certainly one

procedure which we are not at liberty to adopt without valid

justifying reasons, and that is to take one set of those internal

"sensible objects" or "data of awareness," viz. the so-called

primary qualities, size and shape, rest and motion, spatial

continuity and discontinuity or plurality ; to infer from these

the existence of similar qualities in the external domain; to inter

pret the external correlates of the other set of direct objects of

awareness, viz. the so-called secondary qualities, heat, colour,

sound, taste, smell, and tactile data, as modes or varieties of the

external correlates of the former set, i.e. as modes of externally

moving, voluminous or space-filling realities (whether these be

atoms, electrons, dynamic monads, aether, or what not) ; and

thence to conclude that the second set of external correlates, the

secondary qualities as they are externally, being like the first

set because interpreted as modes or varieties of these, are unlike

their own sensible or directly apprehended internal correlates,

viz. sensibly apprehended heat, colour, 1 taste, smell, etc.

1 " It is assumed that there is not even plausibility in the supposition of

continuity or identity between colour proper [i.e. what is present to consciousness

in perception of colour] and its physical conditions in the way of light vibrations."

PRICHARD, op. cit., p. 87 n. If that which we sensibly apprehend as colour be

intellectually conceived and interpreted to be merely vibrations or undulations of

aether in the extramental domain, and we neither affirm nor deny that extramental

colour is or involves this : we leave that question to the physicist and the cos-

mologist ; but if it is so, if extramental colour is rightly conceived and interpreted

intellectually to be or to involve undulations of asther, where is the difficulty in

holding that this same self-identical extramental reality which is intellectually

conceived as aether undulations is sensibly perceived as the object of awareness

which we call colour ? At all events (assuming the truth of some form of realism)

this much at least we know about the extramental reality in question, that it is in

the extramental domain something real which we perceive or apprehend sensibly as

a colour, as red, or blue, or yellow, etc. ; and if perceptionism be true we know

that if the organic conditions of perception be normal the extramental reality is an

external or extra-organic reality sensibly apprehended as red, or blue, or yellow, etc.

How we are to conceive and interpret intellectually the nature of this external

reality the physicist may undertake to discover, while the epistemologist has to

scrutinize the presuppositions of the physicist s hypotheses and methods of induction.

Cf. Art. "Appearance and Reality" in the Irish Ecclesiastical Record, vol. xxiv.

(Sept. 1908), p. 278, n. 2 : " It is sometimes contended . . . that the material energy

or property which we call redness cannot in its own external reality (being an

undulation of the ether) be in any way like our sensation of redness . This shows

a deplorable confusion of sense perception with intellectual conception. The same

reality which we call redness on account of the definite state of sense-conscious

ness aroused in us by the vision of it, we call a property of matter, an active

quality, an energy, a wave-motion on account of the concepts, judgments,

inferences, theories, formed by our intellects, reflecting on the data which that

1 32 THEOR Y OF KNO W LEDGE

Yet this is undoubtedly the procedure which has led many

physical scientists in recent times to build on their perfectly

legitimate scientific hypotheses regarding the nature of light

and heat and sound and other physical realities, such as

chemical, electric and magnetic energies, in the external domain,

the distinctly philosophical and epistemological theory that this

domain consists solely of a reality (?ether) or realities (atoms,

electrons, ions, etc.) endowed with ft\& primary qualities, motion,

volume, continuity or discontinuity, dimensional limits or figures,

etc., and that the secondary sense qualities are subjective, internal,

consciously apprehended effects produced by the primary quali

ties and their insensible modes in the perceiver.

Advocates of this theory must obviously have started by

assuming either that the primary sense qualities themselves, i.e.

consciously apprehended size, shape, figure, motion, rest, unity

and number, or else inferred similar correlates * of these, are real

and actual characteristics of the external domain of reality.

Else what value could their hypotheses have as explanations of

the external domain, since their hypotheses are conceived in

terms of those primary qualities. But if we immediately ap

prehend these as external so do we immediately apprehend the

secondary qualities as external. And if we know the external

primary qualities only by inferring them as similar to internal

directly apprehended correlates, then in the first place it cannot

be said that we know them better than we know these latter ; and

in the second place we not only can infer, but if we are con

sistent we ought to infer, that the external correlates of the

directly apprehended secondary qualities are likewise similar to

these.

It is useless to appeal, with physical realism, to a supposed dif

ferent degree of susceptibility of the perceiver s sense organism,

reality furnishes to those intellects through the medium of sense-consciousness."

Cf. ibid., pp. 278-80.

1 The physical scientist as such usually commences (without troubling himself

with any theory of external perception) by taking for granted, like the plain man,

the external reality of the physical universe and all its sensibly perceived qualities.

Then, with a view to exploring what some or all of the secondary qualities are ex

ternally, e.g. what sound, or light, or heat is externally, he proceeds to assume that

they are (insensible) modes of the primary qualities (e.g. that they are vibratory or

undulatory motions of space-filling atoms or nether, etc.), and to see how his hypo

theses will "work" or "explain the facts," continuing to assume all the time

that these primary qualities are really and externally, and for intellect reflecting on

them, the same as they appear, or similar to what they appear, internally or con

sciously to sense.

PHYSICAL REALISM 133

or a difference in the role played by the brain and nervous system,

in affecting the transition from the sensibly conscious data to

their external correlates, in the two sets of qualities. For since

the whole sense organon is an extramental, material factor, we

cannot say that it presents to consciousness one set of qualities

as they are whether in itself or in the extra-organic domain, or

partly in the one and partly in the other, but in both cases

beyond or independently of consciousness, and another set otherwise

than they are beyond or independently of consciousness. Obviously

we cannot say this without begging the whole question. And

moreover, granting the reality of the role played by the per-

ceiver s sense organon in perception, and the consequent rela

tivity of what is perceived through its functioning, this relativity

must necessarily apply to the primary as well as to the secondary

qualities, for the primary qualities are also sense qualities, and

are apprehended only through the functioning of the various

sense organs.

That the external domain of material reality is characterized only by the

primary qualities, that these are like the correlates of which the perceiver is

directly conscious, that the secondary qualities are really and externally only

modes of the primary qualities, and that as such they are unlike the correlates

which the perceiver directly apprehends as sensible taste, smell, colour, sound,

etc. these assertions are not proved, and cannot be proved, by any scientific

research in the external, physical domain : they are partly assumptions, and

partly inferences from certain ways of using the assumptions. If the

scientist assumes that the primary qualities are really and externally that which

he is directly aware of, or similar to that which he is directly aware of, and if

he then proceeds to interpret the secondary qualities, as external, in terms of

the primary, and supposes them to be insensible modes of the primary, he

will of course have nothing left in the external domain but the primary and

their insensible modes. But he can accept this position only by gratuitously

ignoring the fact that he had the same right, and in consistency the same

duty, to assume that the secondary qualities as objects of direct awareness are

either themselves external or have similar external correlates, or else by as

signing a justifying reason for assuming (cognitive) identity or similarity of the

external with the consciously apprehended data in the case of the primary

qualities and not in the case of the secondary qualities : and this difference of

procedure cannot be justified by any scientific consideration which presup

poses and is dependent on his having made the assumption in the one case

and not in the other. 1 Furthermore, if he accepts the position, he has to

1 And it is exclusively considerations of this kind that are urged from the stand

point of physical science in favour of the view that only the primary qualities of

matter are really and externally as they are perceived. Every such consideration is

a petitio principii.

1 34 THEOR Y OF KNO W LEDGE

accept a conclusion in regard to the secondary qualities which is the direct re

verse of his assumption in regard to the primary qualities, namely, that what

corresponds really and externally to the directly apprehended internal

secondary sense qualities is u?ilike these latter : a conclusion which no con

sideration that is based on his actual assumption can justify.

The secondary qualities, as they exist externally, are qualities of a reality

which has also the primary qualities of extension and motion. Those second

ary qualities have therefore externally a quantitative side. And it is perfectly

legitimate for the physical scientist to conceive and interpret this aspect of

them in terms of the primary qualities, e.g. of extension and motion. But

this does not justify either the scientist or the philosopher in concluding that,

externally, they are merely extension and motion, or that they have not, ex

ternally, the qualitative differences which sense consciousness detects between

visual, auditor} , gustatory, olfactory, and tactual data. When it is said that

for science heat, colour, sound, etc., are motions of extended or space-filling

media (i.e. insensible motions of insensible media, but conceived after the

analogy of sensible motions of sensible media) ; that therefore they are really

such and cannot be as they are perceived by sense to be ; that as perceived

by sense they must be only (organic or mental) states of the perceiver, these

inferences far outrun their premisses. For if the scientist abstracts from the

manner in which the secondary qualities appear to sense and conceives them

after the analogy of the primary qualities (assuming that these really are as

they appear to sense), if in other words he conceives only their quantitative

or extension-and-motion aspects, then even if his interpretation of their ex

ternal reality or nature be right as far as it goes, even if they are really as he

conceives them intellectually after the analogy of extension-and-motion, it by

no means follows that such intellectual conception of them is adequate, that

they have not also externally the secondary or qualitative aspect which they are

apprehended by sense as having, or that these secondary, qualitative aspects

are only internal states produced in the perceiver by heterogeneous moving

and space-filling realities. 1 On the contrary, if the scientist s assumption that

the external primary qualities are intellectually and really, by identity or

similarity, what they are sensibly apprehended to be, consistency with this

assumption would demand the same for the external secondary qualities.

We may be right e.g. in intellectually conceiving " red " as an insensible

external aether undulating 482,000,000,000 times per second. But since our

concepts of aether and undulations are derived from the data directly present

to sense consciousness in our perceptions of sensibly extended or space-filling

and sensibly moving matter, or in other words from primary sense qualities

assumed to be either themselves externally real or to represent similar ex

ternal realities, and since these concepts are externally valid only on the

assumption that our perception of extension and motion validly presents or re

presents these external primary qualities, it is clear that these concepts, when

they are used to interpret the external correlate of the "red" which is present

to consciousness, even though they be proved to be validly applicable to this

"external red" (or external correlate of what is present to consciousness as

" red)," cannot adequately represent the external reality of " redness," but only

1 Cf. Science of Logic, ii., 228, pp. 127-35 ; Ontology, n, pp. 70-1.

PHYSICAL REALISM 135

the quantitative, aether-and-undulation (or insensible extension-and-motkm)

aspect of it. There is another intellectually conceived aspect of it which we

have an equal right to regard as externally real, namely, that which is pre

sented or represented in the concrete percept, " red," which is present to our

visual sense consciousness. For if we hold that sensibly perceived extension

and motion (from which we derive our concepts of external aether and ex

ternal undulations) are externally real, or have externally real correlates

similar to themselves, we have an equal right to hold that sensibly perceived

redness (from which we derive our concept of redness as an external quality)

is itself externally real or has an externally real correlate similar to itself. To

say, therefore, that because external redness is validly conceived by " quanti

tative " concepts as externally undulating aether, it cannot be also validly con

ceived by the " qualitative " concept which represents it as a something external

sensibly apprehended as red, is not only to confound abstraction with negation,

but also to accept the external validity of derivative concepts (aether and un

dulations), 1 and the propriety of their application to explain the real nature of

the external reality sensibly apprehended as " red," and at the same time to

deny the external validity of the direct intellectual concept for which the deriva

tive concepts were substititfed, namely, the intellectual concept of " redness,"

although this concept has precisely the same claim to external validity as the

direct concepts of extension and motion from which the concepts of aether and

undulations were derived. For all three concepts, "extension," "motion,"

and " redness," are abstracted from specific concrete sense data immediately

present to sense consciousness with the common characteristic of felt externality.

It may, perhaps, be true that the external reality of "redness" involves

insensible aether undulating at a certain rate, and we may perhaps be said to

know this ; but we cannot be said to know that the external reality of redness

is this alone, or to know the external reality of insensible aether and undula

tions better than we know e.g. a field of poppies to be really external to us and

to have a characteristic or quality the reality of which consists partly at least

(whatever be its total reality) in appearing to our sense consciousness in ex

ternal perception as " redness ". Yet it is a common procedure with many

modern writers on sense perception to start from the nature of external

physical realities as conceived by scientists through such quantitative concepts

as those of atoms, electrons, aether, undulations, etc., concepts formed from

the primary sense qualities as present to consciousness, and to infer that be

cause the external correlates of the secondary sense qualities present to con

sciousness have been interpreted by scientists through such concepts, and

when so interpreted are of course unlike these secondary or proper sensibles,

therefore these latter, as perceived, cannot be in the external domain at all,

but must be merely organic or psychic states of the perceiver. Such writers

attribute to physical science an achievement of which it is innocent : they

seem to think that it has made us more certain of the external reality of atoms,

electrons, aether, undulations, etc., than we are of the external reality of

sensibly perceived motion, extension, shape, number, etc., from the (primary

sense] percepts of which those concepts have been formed; and more certain

1 I.e. derived from the concepts of extension and motion, which latter concepts

were in turn abstracted from concrete sensibly apprehended extension and motion.

1 36 TtlF.OR \ OF UNO WLRDGft

that those concepts, applied to the external correlates of our secondary sense

percepts, represent to us faithfully (or even adequately) the nature of the ex

ternal correlates of these secondary sense percepts, than we are that those

external correlates are externally as they are presented in our secondary sense

percepts and represented by the concepts formed from these. But physical

science has thrown, and can throw, no such light on the problem of sense

perception (112). And if by abstracting from what we may call the qualita

tive aspects of external physical realities, the aspects revealed in the proper or

secondary sense qualities, and fixing its attention on iht\r quantitative aspects,

the aspects revealed in the common or primary sense qualities, because these

are found more amenable to its exact, quantitative calculations, hypotheses, and

methods of experiment and verification, 1 science has thus achieved notable

triumphs of discovery which give us ever-increasing power over the manipula

tion of physical forces, it is nevertheless the duty of the epistemologist to ex

plore the epistemological presuppositions of physical science. It is his duty

to examine the grounds of the validity of the concepts used by it ; to look into

its application of these concepts ; to point out especially that its procedure of

accepting the externality of the common sensibles (and the external validity

of direct and derivative concepts based on them) and abstracting from the

externality of the proper sensibles (and from the external validity of the con

cepts based on these), does not at all imply negation of the external validity

of these latter percepts and concepts, or involve the contention that secondary

sense qualities and qualitative differences are merely internal states of the

sentient perceptive subject. It is his duty to show that the transference of

secondary qualities from the external to the internal domain is by no means

a proof that these are merely internal, but only a conclusion from the procedure

of applying "inference by similarity " to the primary qualities alone and not

to the secondary, and at the same time mistaking abstraction from what this

inference would yield concerning the secondary qualities, for negation of a

similar external counterpart of these latter ; and to note, finally, that since

physical science can never hope to show why or how e.g. 482,000,000,000

vibrations of ;cther per second produces the internal sensation of "red," it

merely hands over this and similar data unexplained to the physiologist or the

psychologist. -

If the secondary sense qualities, as they are conceived to be externally

1 Cf. Science of Logic, ii., 243, 246, 224 (pp. 110-12).

- The sense perception of " redness," or of any other sense quality, is, of course,

like the fact of knowledge itself, an ultimate, unanalysable fact which cannot be

" explained " in terms of anything simpler than itself. Yet some writers seem to

think that they are called upon to " explain " such facts; and some physical scien

tists seem to think that they have " explained " " redness " by stating that it is ex

ternally a certain rate of undulations of aether, and that it is internally a (psychic or

organic) state of a certain conscious tone or quality which we feel and name as

" redness," and which is the only internal state that the external rate of aether-un

dulation can produce. No scientist has of course ever " explained " why just this

undulation-rate produces just this definite sort of internal state ; nor is any scientist

called upon to explain what, if it be a fact, is an ultimate fact. Yet some scientists

appear to think that it is " explainable," and that their theories cannot be held as

verified so long as they fail to explain it. Cf. passage quoted from Sir John Her-

schel s Discourse on Natural Philosophy, apiul CASE, of. cit., p. 12.

PHYSICAL REALISM 137

by the physical scientist, are unlike what they appear internally, this is merely

because the scientist has conceived them after the analogy of primary internal

sense data and their supposed similar external correlates, to which the in

ternal secondary qualities consciously bear no resemblance. He has not

proved but assumed that there is similarity between the " internal " and the

"external," or the "apparent" and the "real," in the one case, and dis

similarity in the other. If what is external can be known only by inference

(on the principle of similarity) from the internal, then it is surely an inversion

of the facts to assume, as Professor Case seems to assume, that we know the

external better than the internal : that we know what the secondary qualities

are externally, or as "physical objects of science," better than we know what

they are internally or as " data of sense ". :

For the reasons already given this line of thought is unconvincing, (i)

It is not proved that the external cannot be immediately perceived. (2) Not

only for the child 2 but for the man, not only for the physical scientist but for

the psychologist and the epistemologist, " sensible data are the causa cognos-

cendi " of whatever can be known about the whole material domain, whether

internal or external. (3) The author nowhere proves those sensible data to

be states of the nervous system, and even if he did that would not explain

our awareness of them, for the possibility of awareness of a state of the self is

no less mysterious than the possibility of awareness of a state of the non-self.

(4) Seeing that scientists are supposed on this theory to infer " the physical

objects of science " from one section of our sensible data by the law of

" similarity," it cannot be maintained that the external reality of these objects

is " better known " than the sensible data from which they are inferred, or

that we should start from the former in investigating the validity of sense per

ception. In modern times many " scientific " theories have been propounded

concerning the existence and nature of the aether, molecules, atoms, etc. ;

concerning light, colour, heat, as modes of motion of these entities ; concern

ing the interpretation of secondary qualities in the external domain as specific

varieties of the primary qualities s ; concerning the reducibility of all qualitative

differences in this domain to quantitative differences, i.e. to different modes of

motion of a quantitative, voluminous, extended material substrate, whether

atomic (discontimtous) or continuous, or in other words to differences of

primary qualities ; concerning the consequent and necessary banishment of

the secondary qualities as such to the internal domain of the perceiving sub

ject. But surely, when we approach the epistemological problem What is

the nature of those data of sense awareness ? Are they internal or external ?

Are they self or non-self? Are they extramental, physical realities, or mind-

dependent, psychic states ? it is an inversion of right method to seek the

solution of this problem by assuming as certain the external reality of those

qualities, and those alone, which scientists regard as externally real, without

inquiring into the validity of the presuppositions and processes whereby

scientists have come to regard them, and them alone, as externally real.

Some of Professor Case s criticisms of Idealism are unexceptional, and indeed

unanswerable. But his own position misconceives the role of the perceiver s

organism in the perceptive process, while his adoption of representationism

1 Cf. op. cit., pp. 27-8, 35-9. z lbid., p. 36. 2 Ibid., pp. 23, 29.

1 38 THEOR Y OF KNO WLEDGE

and inference by similarity leaves that position exposed to some of the main

difficulties against Idealism itself. It has not been proved, but assumed, by

representationists that the internal effect of the external quality is the produc

tion, in the perceiver, of a directly apprehended datum (organic or psychic)

similar to itself. May not the effect produced internally by the external

quality be rather the con scions perception of this hitter itself , as perceptionists

contend ? At all events if the principle of inference by similarity be applied

at all, it should be applied to perception of secondary no less than of primary

qualities, unless valid reason be shown for not applying it to the former. And

so far from such reason having been shown, idealists have not been slow to

point out that if such inference be not applicable to secondary qualities

neither can it yield certitude about the external nature of primary qualities,

and that we should therefore consistently adopt the transfigured or symbolic

realism of Spencer, or the cosmothetic, hypothetical realism of Kant, or else

candidly confess with Idealism itself that extramental reality is wholly

problematic and therefore unknowable.

Before indicating this historical line of speculation we may here observe

that if we have dwelt at such length, in the present section, on Physical

Realism, and on the bearing of current physical theories regarding the external,

material domain, upon the general problem of sense perception, our object

has been to counteract the widely prevalent impression that because phy

sical theories have wrought such unparalleled achievements in the external

domain, they have also yielded, in regard to the nature and objects, and the

scope and limits, of sense perception, certain revolutionary inferences which

must be accepted without exploring the presuppositions, in regard to percep

tion, on which these inferences are based. It is throwing no discredit on

physical science to say that such an impression is erroneous and mischievous :

physical science is not accountable for it : it is not entertained by really

scientific minds : reflecting scientists are aware of the epistemological assump

tions underlying their theories, and of the dependence (for validity) of the

latter upon the former ; and they would be the last to deny to the inquirer

into the knowledge-value of sense perception the right to explore these per-

suppositions and thereby to appraise the real knowledge-value of the theories

based upon them.

CHAPTER XIX.

SUBJECTIVE IDEALISM, INFERENTIAL REALISM, AND INTUITIVE

REALISM.