hearing and listening, between seeing and looking, so must we distinguish between touching and palpation.

Mere passive touch gives a certain amount of information, but comparatively little. It is necessary to explore; that is what is done in active touch—palpation—of different degrees.

The sensitiveness of the skin varies at different places from the tongue downwards. Palpation by the fingers marks a further stage. The blind also, we are told, largely employ the feet in walking as a source of locative data.

To the concepts reached by such palpation with the hand, M. Villey gives the name of Manual Space. In this connection he thinks it necessary to distinguish between synthetic touch and analytic touch—the former resulting from the simultaneous application of different parts of the hand on the surface of a body, the latter that which we owe to the movements of our fingers when having only one point of contact with the object the fingers follow its contour. Various examples of the delicacy of the information thus obtainable are given. Following two straight lines with the thumb and index respectively, a blind man can acquire by practice a sensibility so complete as to enable him to detect the slightest divergence from parallelism.

The analysis passes on from the data of Space manual to those of Space brachial; then to the information derived from walking and other movements of the lower limbs, and then to the co-ordination of the information derived from the sensations of hearing, which is necessarily very important to the blind.

The conclusion of the whole matter is that our principal spatial ideas are common alike to the blind and the vident. Both can be taught and are taught the same geometry. Both understand one another in the description of spatial conditions. The common element cannot possibly be supplied either by the data of visual sensation which the blind do not possess, or by the data of passive tactual sensation which the vident hardly ever employ. Une étendue commune se retrouverait à la fois dans les données de la vue et dans celles du toucher. The common element is furnished by the common laws and forms of our exertional Activity by means of which and in terms of which we all construct our conceptions of the dynamic world of our environment.

It is from our dynamic Activity also that we derive our conception of Force. Force, though it is studied scientifically in the measurement of the great natural forces which operate constantly, is originally known to us in the stress or pressure to which muscular exertion in contact with a material body gives rise. Such a force if it could be correctly measured, would record the rate at which Energy was undergoing transmutation, and it is from such experience of pressure that our idea of Force is originally derived.

The mass of bodies is usually measured by their weight, i.e. by gravity. Its absolute measurement must be in terms of momentum. The true estimate of the Energy of a body moving under the impulse of a constant Force is stated in the formula 1/2MV². To ascertain M, therefore, we must have given F and V, and these are both conceptions the original idea of which is derived from our exertional activity.

Quantity of Matter originally means the same as amount of resistance to initiation of motion, at first estimated by the varying amount of personal muscular energy required to effect the motion in question, thereafter objectively and scientifically by comparison with some independent standard whereby a more exact estimation can be attained than was possible by a mere reference to the varying inferences of the individual who might exert the force.

Space, Mass, Force are all therefore ideas which are furnished to us out of our experience as potent actors, and the recognition of this great truth provides us with the means of clearly apprehending and co-relating our conceptions of the external world, the framework of our Knowledge.

The true distinction between a percept and a concept is just that a percept is a concept associated with the dynamic system discovered in and by our exertional activity.

In like manner we find here the true solution of the many questions which have been raised as to the distinction between general and abstract, singular and concrete terms.

Language expresses action: the roots of language are expressions of the elementary acts which make up experience. They are therefore general. Each applies to every act of the class in question. They are also concrete. That is so because they refer to exertional activities. Abstract terms are terms abstracted from this dynamic reference. Thus white is concrete because colour is a property of the dynamic world. But when this property is considered apart from its dynamic support it is called whiteness, and becomes abstract. In the case of purely mental qualities the term is regarded as abstract simply because the quality is in every reference extra dynamic. Thus candour, justice are called abstract terms; they are properties of the Mind. But a property of the dynamic system, e.g. Gravitation, does not strike us as abstract—the sole distinction being the dynamic reference which the latter term implies.

It will even be seen that there is sometimes a shading off of abstract quality. Thus Justice as an attribute of the Mind strikes us as a purely abstract term. But as the word takes up a dynamic reference so does its abstraction diminish. Thus in the expression "Administration of Justice" the abstractive suggestion is less pronounced; till in the person of Justice Shallow it vanishes in the very concrete.

Behind and beneath all these considerations we should never lose sight of the great main facts—that thought is an activity; that its function therefore is to represent or reproduce our pure exertional activity; that such representation is at the basis of all our concepts of externality; that sensation, per se is mere interruption of activity; that per se it possesses no spatial or extensive or external suggestiveness; that sensations nevertheless serve to denote or give feature and particularity to our experience of activity; that all perception of the external is at bottom therefore a mental representation of exertional activity and its forms, denoted, punctuated, identified by sensation, which latter by itself, we repeat, carries no suggestion of externality. This view revolutionises the whole psychology of Perception, and therefore, though it at once gives to that science a much-needed unity, clarity, and simplicity, it will naturally be accepted with reluctance by the laborious authors of the cumbrous theories still generally current.

FOOTNOTES:

III

THE TWO TYPICAL THEORIES OF KNOWLEDGE

The evolution of living organisms is in general a gradual and continuous process. But it is nevertheless true that it presents well-marked stages and can best be described by reference to these. Frequently, moreover, the meaning and true nature of the movement at one stage is only