METHOD OF MULTIPLE WORKING HYPOTHESES 841 
theme is but the progressive dominance of a ruling idea. Briefly 
summed up, the evolution is this: a premature explanation passes 
first into a tentative theory, then into an adopted theory, and 
lastly into a ruling theory. 
When this last stage has been reached, unless the theory 
happens perchance to be the true one, all hope of the best results 
is gone. To be sure truth may be brought forth by an investi- 
gator dominated by a false ruling idea. His very errors may 
indeed stimulate investigation on the part of others. But the 
condition is scarcely the less unfortunate. 
As previously implied, the method of the ruling theory occu- 
pied a chief place during the infancy of investigation. It is an 
expression of a more or less infantile condition of the mind. I 
believe it is an accepted generalization that in the earlier stages 
of development the feelings and impulses are relatively stronger 
than in later stages. 
Unfortunately the method did not wholly pass away with the 
infancy of investigation. It has lingered on, and reappears in 
not a few individual instances at the present time. It finds illus- 
tration in quarters where its dominance is quite unsuspected by 
those most concerned. 
The defects of the method are obvious and its errors grave 
If one were to name the central psychological fault, it might be 
stated as the admission of intellectual affection to the place 
that should be dominated by impartial, intellectual rectitude 
alone. 
So long as intellectual interest dealt chiefly with the intangi- 
ble, so long it was possible for this habit of thought to 
survive and to maintain its dominance, because the phenom- 
ena themselves, being largely subjective, were plastic in the 
hands of the ruling idea; but so soon as investigation turned 
itself earnestly to an inquiry into natural phenomena whose 
manifestations are tangible, whose properties are inflexible, and 
whose laws are rigorous, the defects of the method became 
manifest and an effort at reformation ensued. The first great 
endeavor was repressive. The advocates of reform insisted that 
