Fig. 11If we have a beaker full of sugar solution we can change the sugar into alcohol by in-
oculating the solution with a certain kind of ferment, we can change it inio a mixture
of glucose and fructose by adding hydrochloric acid, we can change it into carbon by
adding strong sulphuric acid and so on. All these different kinds of changes can be
brought about by producing different conditions, by applying different kinds of stimuli
for the manifestation of different potentialities. But the potentialities for all these
changes already exist in the sugar solution. We cannot, for instance, change the sugar
into mercury because there is no potentiality, in the chemical sense, for sugar to
change into mercury.
The incidental or existing cause which seems outwardly to bring about the
change is not the real cause of the change. The change is really brought about by the
predisposing causes determined by the nature of potentialities existing in the things
undergoing change. What the incidental cause does is merely to determine in which
direction change will take place and thus to direct the flow of natural forces in that
particular direction.
The respective role of the exciting and predisposing causes in bringing about all
kinds of changes in Nature is then further made clear by the use of a very apt simile
“like a farmer”. Anyone who has observed a farmer directing the current of water into
different parts of a field will see at once how closely such a process resembles the ac-
tion of natural forces being directed by one or the other of the outward causes which
seem to bring about different kinds of changes. He removes a little earth here and the
water begins to flow in one furrow. Then he closes up the gap and makes a breach at
another place and the water begins to flow in another direction. The removal of a little
earth from one particular spot does not produce the current of water. It merely removes
an obstacle in the path of the water and determines the direction of the current.