i 
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 
go 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, 
