224 THE PRESENT IMPORTANCE OF SCIENCE 



and the objective, taking it in the sense of what is within and 

 what is outside ourselves, the / as distinct from that which 

 is not myself. We know the subjective element, because we 

 are conscious of our own existence and of our mental proc- 

 esses. Hence there is one class of facts which is subjective 

 in origin and another which originates in sense-impressions 

 which are assumed to be induced by an objective or external 

 reality. We know the objective element solely through these 

 impressions of our sense-organs. The ego is like a telephone 

 operator shut in a central office and knowing nothing of the 

 outside world save by what comes in through the receivers. 

 To the objective or natural sciences, sense-impressions are 

 the ultimate reality upon which must be based any theory 

 of an external universe of matter. 



We may pursue the case as follows : A man has reason for 

 believing, because of what he sees in bodies like his own, that 

 his particular human body presents anatomical and physi- 

 ological phenomena of the kind demonstrable in other 

 human beings and in the higher vertebrates. The individual 

 knows his own conscious existence first hand, and infers 

 the existence of everything else. Granting that / know I 

 exist, and you know you exist, and that we can each infer 

 that the other exists, how do we draw such an inference and 

 what do we mean when we say that this or any other infer- 

 ence has scientific validity? 



We know the outer world only through the medium of our 

 sense-organs. You see a book before you, with its red cover, 

 gilt letters, and white leaves; it feels hard; it creates a noise 

 when dropped; it smells like a book fresh from the bindery. 

 If you desire yet another form of sense-impression, you 

 may taste the cover or the leaves, as you perhaps remember 

 doing when a boy at school, and so experience the last type 

 of first-hand knowledge which is presented by the more 

 familiar senses. You know that such an object as the book 

 exists only by these evidences derived from your sense- 

 organs and termed sense-impressions. You have learned 



