+ PTE a Lo ee 
TRANSACTIONS OF SEGTION A, 617 
may appear strange to us now that we have finished the journey, though no doubt 
it was inevitable, the purpose and will of which the laws had been the expression 
were put into the laws themselves; they were personified and made to will 
and act. 
Even now these early stages in the history of thought can be traced by 
survivals in our language, survivals due to the ascription of moral qualities to 
matter. Thus gases are still sometimes said to obey or to disobey Boyle’s Law as if 
it were an enactment for their guidance, and as if it set forth an ideal, the perfect 
gas, for their imitation, We still hear language which seems to imply that real 
gases are wanting in perfection, in that they fail to observe the exact letter of the 
law. I suppose on this view we should have to say that hydrogen is nearest to 
perfection; but then we should have to regard it as righteous overmuch, a sort of 
Pharisee among gases which overshoots the mark in its endeavour to obey the law. 
Oxygen and nitrogen we may regard as good enough in the affairs of everyday 
life. But carbon dioxide and chlorine and the like ara poor sinners which yield 
to temptation and liquefy whenever circumstances press at all hardly on them, 
There is a similar ascription of mora] qualities when we judge bodies accord- 
ing to their fulfilment of the purpose for which we use them, when we describe 
them as good or bad radiators, good or bad insulators, as if it were a duty on their 
part to radiate well, or insulate well, and as if there were failures on the part of 
Nature to come up to the proper standard. 
These are of course mere trivialities, but the reaction of language on thought 
is so subtle and far-reaching tbat, risking the accusation of pedantry, I would 
urge the abolition of all such picturesque terms. In our quantitative estimates let 
us be content with ‘high’ or ‘ low,’ ‘ great’ or ‘small,’ and let us remember that 
there is no such thing as a failure to obey a physical law. A broken law is 
merely a false description. 
Concurrently with the change in our conception of physical law has come a 
change in our conception of physical explanation. We have not to go very far 
back to find such a statement as this—that we have explained anything when we 
know the cause of it, or when we have found out the reason why—a statement 
which is only appropriate on the psychical view. Without entering into any dis- 
cussion of the meaning of cause, we can at least assert that that meaning will only 
have true content when it is concerned with purpose and will. On the purely 
physical or descriptive view, the idea of cause is quite out of place. In descrip- 
tion we are solely concerned with the ‘how’ of things, and their‘ why’ we pur- 
posely leave out of account. We explain an event not when we know ‘why’ it 
happened, but when we show ‘ how’ it is like something else happening elsewhere 
or otherwhen—when, in fact, we can include it as a case described by some law 
already set forth. In explanation, we do not account for the event, but we im- 
prove our account of it by likening it to what we already knew. 
For instance, Newton explained the falling of a stone when he showed that 
its acceleration towards the earth was similar to and could be expressed by the 
same law as the acceleration of the moon towards the earth. 
He explained the air disturbance we call ‘sound’ when he showed that the 
on and forces in the pressure waves were like motions and forces already 
studied. 
Franklin explained lightning when and so far as he showed that it was similar 
in its behaviour to other electric discharges. 
Here I do not fear any accusation of pedantry in joining those who urge that 
we should adapt our language to the modern view. It would be a very real gain, 
_a great assistance to clear thinking, if we could entirely abolish the word ‘cause’ 
in physical description, cease to say ‘why’ things happen unless we wish to 
signify an antecedent purpose, and be content to own that our laws are but 
expressions of ‘how’ they occur. 
The aim of explanation, then, is to reduce the number of laws as far as possible, 
by showing that laws, at first separated, may be merged in one ; to reduce the number 
of chapters in the book of science by showing that some are truly mere sub-sections 
of chapters already written. 
