186 STONEY—UNIVERSE OF REAL EXISTENCES. [April 3, 
existences and real activities of which the true universe actually 
consists: which is the problem we proposed to investigate. 
. CHAPTER 18. Or PuysICAL CAUSES AND OF EFFICIENT CAUSES. 
Causation, in the full sense of that term, implying efficiency in 
the cause, can only prevail in the operations of auta. 
When an efficient cause operates within the sense-compelling 
universe, it produces some change therein, and if this change be 
such that the sense-compelling universe can produce one set of 
effects within human minds before the change and another set after 
the change, then will the hypothetical existence which we call 
nature also undergo a change. ‘This is because nature before the 
change is the syntheton made by fitting together the former set of 
possible effects, and nature after the change is the syntheton of the 
latter set of possible effects. We may liken the sense-compelling 
universe to a mighty machine, and nature to a shadow cast by it in 
a very special way. If the machine is set in motion and changed 
from one position to another, it produces one shadow before the 
change and another after; and if the change in the machine has 
followed a definite order, the second shadow will succeed the first 
in a corresponding orderly sequence: but the relation between the 
shadows is not the relation of cause and effect. 
Accordingly, in the laws of Nature which have been discovered 
by scientific investigation we find abundant instances of unfailingly 
concomitant events and of uniformities of sequence, but not a single 
instance of genuine cause and effect. The so-called Physical causes 
’ are not causes in the full sense of that term. We might write them as 
[causes |’ with a dash, but not as [causes] without one. Nevertheless 
it is Jegitimate as an hypothesis, to treat them as though they were 
causes when and so long as we are engaged in making use of the 
Objective Hypothesis. If a stone be allowed to drop in the vicin- 
ity of the earth, its downward speed is accelerated by a perfectly 
definite law. In this case the vicinity of the earth to the stone and 
the acceleration of the stone’s vertical velocity are two unfailingly 
concomitant events. This is one of the Uniformities of Nature 
which scientific inquiry has brought to light. But w¢thin the domain 
of Physics there is no cause for the acceleration. To reach the 
cause we must travel beyond the hypothetical domain of Physics 
and study the events that have taken place in the universe of real 
