THE FACTS OF SCIENCE 69 



^ 1 4. — Shadoiv mid Reality 



The reader who comes to these problems for the first 

 time may feel inclined to assert that if this world of sense- 

 impressions is the world of scientific knowledge, then 

 science is dealing with a world of shadows and not of real 

 substances. And yet, if such a reader will think over 

 what happens when he knocks his elbow against the table, 

 I think he will agree that it is the sense-impressions of 

 hardness, and perhaps of pain, which are for him the 

 realities, while the table, as a " source of these sense- 

 impressions," is the shadow. Should he impatiently retort : 

 " I see the table — four-legged, brass-handled, with black 

 oak top shining under the elbow-grease of a past genera- 

 tion — there is the reality," let him stop for a moment to 

 inquire whether his reality is not a construct from im- 

 mediate and stored sense-impressions, of exactly the same 

 character as the previous sense -impression of hard- 

 ness. He will soon convince himself that the real table 

 lies for him in the permanent association of a certain 

 group of sense-impressions, and that the shadow table is 

 what might be left were this group abstracted. 



Let us return for a moment to our old friend the 

 blackboard, represented for us by a complex of properties 

 (p. 40). In the first place we have size and shape, then 

 colour and temperature, and, lastly, other properties like 

 hardness, strength, weight, etc. Clearly the blackboard 

 consists for us in the permanent association of these pro- 

 perties, in a construct from our sense-impressions. Take 

 away the size and shape, leaving all the other properties, 

 and the group has ceased to be the blackboard, whatever 

 else it may be. Suppose the colour to go and again the 

 blackboard has ceased to be. Finally, if the hardness and 

 weight were to vanish, we might see the ghost of a black- 

 board, but we should soon convince ourselves that it was 

 not the " reality " we had termed blackboard. Now, as 

 the reader may be thinking that this blackboard has had 

 too long an existence, at least in our pages, let us employ 

 a carpenter to pull it to pieces and construct out of it a 



