6 Darwin, and after Darwin. 
Well, in the second place, Darwin has shown that 
next only to the importance of clearly distinguishing 
between facts and theories on the one hand, and of 
clearly recognising the relation between them on the 
other, is the importance of not being scared by the 
Bugbear of Speculation. The spirit of speculation is 
the same as the spirit of science, namely, as we have 
just seen, a desire to know the causes of things. The 
hypotheses non fingo of Newton, if taken to mean what 
it is often understood as meaning, would express 
precisely the opposite spirit from that in which all 
scientific research must necessarily take its origin. 
For if it be causes or principles, as distinguished from 
facts or phenomena, that constitute the final aim of 
scientific research, obviously the advancement of such 
research can be attained only by the framing of 
hypotheses. And to frame hypotheses is to specu- 
late. 
Therefore, the difference between science and specu- 
lation is not a difference of spirit ; nor, thus far, is it 
a difference of method. The only difference between 
them is in the subsequent process of verifying hypo- 
theses. For while speculation, in its purest form, is 
satisfied to test her explanations only by the degree 
in which they accord with our subjective ideas of prob- 
ability—or with the “ Illative Sense” of Cardinal New- 
man,—science is not satisfied to rest in any explanation 
as final until it shall have been fully verified by an 
appeal to objective proof. This distinction is now so 
well and so generally appreciated that I need not 
dwell upon it. Nor need [ wait to go into any details 
with regard to the so-called canons of verification. 
My only object is to make perfectly clear, first, that 
