THE FACTS OF SCIENCE 41 



Americans, and with ships and chattels coming from 

 America, which lead me to believe in the " reality " of 

 America and of what my eyes or ears have told me of its 

 contents. In constructing the Capitol it is clear that past 

 experience of a variety of kinds is largely drawn upon. 

 But it must be noted that this past experience is itself 

 based upon sense-impressions of one kind or another. 

 These sense-impressions have been as it were stored in the 

 memory. A sense-impression, if sufficiently strong, leaves 

 in our brain some more or less permanent trace of itself, 

 which is rendered manifest in the form of association 

 whenever an immediate sense-impression of a like kind 

 recurs. The stored effects of past sense-impressions 

 form to a great extent what we are accustomed to 

 speak of as an " external object." On this account 

 such an object must be recognised as largely constructed 

 by ourselves ; we add to a greater or less number of 

 immediate sense-impressions an associated group of stored 

 sense-impressions. The proportion of the two contribu- 

 tions will depend largely on the keenness of our organs 

 of sense and on the length and variety of our experience. 

 Owing to the large amount we ourselves contribute to 

 most external objects, Professor Lloyd Morgan, in the 

 able discussion of this matter in his Animal Life and 

 Intelligence (p. 3 12), proposes to use the term construct 

 for the external object. For our present purpose, it is 

 very needful to bear in mind that an external object 

 is in general a construct — that is, a combination of 

 immediate with past or stored sense-impressions. The 

 reality of a thing depends upon the possibility of its 

 occurring in whole or part as a group of immediate 

 sense-impressions.^ 



1 The division between the real and unreal, and again between the real 

 and ideal, is less distinct than many may think. For example, the planet 

 Neptune passed from the ideal to the real, but the atom is still ideal. The 

 ideal passes into the real when its perceptual equivalent is found, but the 

 unreal can never become real. Thus the concepts of the metaphysicians, 

 Kant's thiiio- in itself ox Clifford's iniiid stuff, are in my sense of the words 

 unreal (not ideal), they cannot become immediate sense-impressions, but the 

 physical hypotheses as to the nature of matter are ideal (not unreal), for they 

 do not lie absolutely outside the field of possible sense-impressions. 



