J 



4 INTRODUCTION. 



tions, while the latter are independent of any such in- 

 herited adjustment of special mechanisms to the exi- 

 gencies of special circumstances. Reflex actions under 

 the influence of their appropriate stimuli may be com- 

 pared to the actions of a machine under the manipu- 

 lations of an operator ; when certain springs of action 

 are touched by certain stimuli, the whole machine is 

 thrown into appropriate movement ; there is no room for 

 choice, there is no room for uncertainty ; but as surely as 

 any of these inherited mechanisms are affected by the 

 stimulus with reference to which it has been constructed 

 to act, so surely will it act in precisely the same way as it 

 always has acted. But the case with conscious mental 

 adjustment is quite different. For, without at present 

 going into the question concerning the relation of body 

 and mind, or waiting to ask whether cases of mental 

 adjustment are not really quite as "mechanical in the 

 sense of being the necessary result or correlative of a chain 

 of physical sequences due to a physical stimulation, it is 

 enough to point to the variable and incalculable character 

 of mental adjustments as distinguished from the constant 

 and foreseeable character of reflex adjustments. All, in 

 fact, that in an objective sense we can mean by a mental 

 adjustment is an adjustment of a kind that has not been 

 definitely fixed by heredity as the only adjustment pos- 

 sible in the given circumstances of stimulation. For were 

 there no alternative of adjustment, the case, in an animal 

 at least, would be indistinguishable from one of reflex 

 action. 



It is, then, adaptive action by a living organism in 

 cases where the inherited machinery of the nervous system 

 does not furnish data for our prevision of what the adap- 

 tive action must necessarily be — it is only here that we 

 recognise the objective evidence of mind. The criterion 

 of mind, therefore, which I propose, and to which I shall 

 adhere throughout the present volume, is as follows : — 

 Does the organism learn to make new adjustments, or to 

 modify old ones, in accordance with the results of its own 

 individual experience ? If it does so, the fact cannot be 

 due merely to reflex action in the sense above described, 



