12 
INTRODUCTION 
defining instinct in a manner which shall be formally 
exclusive, on the one hand of reflex action, and on the 
other of reason. As Virchow truly observes, 6 it is diffi- 
cult or impossible to draw the line between instinctive 
and reflex action ; 5 but at least the difficulty may be 
narrowed down to deciding in particular cases whether 
or not an action falls into this or that category of defini- 
tion ; there is no reason why the difficulty should arise 
on account of any ambiguity of the definitions themselves. 
Therefore I endeavour to draw as sharply as possible the 
line which in theory should be taken to separate in- 
stinctive from reflex action ; and this line, as I have 
already said, is constituted by the boundary of non-mental 
or unconscious adjustment, with adjustment in which 
there is concerned consciousness or mind. 
Having thus, I hope, made it clear that the difficulty 
of drawing a distinction between reflex and instinctive 
actions as a class is one thing, and that the difficulty of 
assigning particular actions to one or the other of our 
categories is another thing, we may next perceive that the 
former difficulty is obviated by the distinction which I 
have imposed, and that the latter only arises from the fact 
that on the objective side there is no distinction im- 
posable. The former difficulty is obviated by the distinc- 
tion which I have drawn, simply because the distinction 
is itself a definite one. In particular cases of adjustive 
action we may not always be able to affirm whether con- 
sciousness of their performance is present or absent ; but, 
as I have already said, this does not affect the validity of 
our definition ; all we can say of such cases is that if the 
performance in question is attended with consciousness it 
is instinctive, and if not it is reflex. 
And the difficulty of assigning particular actions to one 
or other of these two categories arises, as I have said, 
merely because on the objective side, or the side of the 
nervous system, there is no distinction to be drawn. 
Whether or not a neural process is accompanied by a men- 
tal process, it is in itself the same. The advent and de- 
velopment of consciousness, although progressively con- 
verting reflex action into instinctive, and instinctive into 
