INTRODUCTION. 
5 
for it is impossible tiiat heredity can have provided in 
advance for innovations upon, or alterations of, its machi- 
nery during the lifetime of a particular individual. 
In my next work I shall have occasion to consider this 
criterion of mind more carefully, and then it will be 
shown that as here stated the criterion is not rigidly ex- 
clusive, either, on the one hand, of a possibly mental 
element in apparently non-mental adjustments, or, con- 
versely, of a possibly non-mental element in apparently 
mental adjustments. But, nevertheless, the criterion is 
the best that is available, and, as it will be found sufficient 
for all the purposes of the present work, its more minute 
analysis had better be deferred till I shall have to treat of 
the probable evolution of mind from non-mental an- 
tecedents. I may, however, here explain that in my use 
of this criterion I shall always regard it as fixing only the 
upper limit of non-mental action ; I shall never regard it 
as fixing the lower limit of mental action. For it is clear 
that long before mind has advanced sufficiently far in the 
scale of development to become amenable to the test in 
question, it has probably begun to dawn as nascent sub- 
jectivity. In other words, because a lowly organised 
animal does not learn by its own individual experience, 
we may not therefore conclude that in performing its 
natural or ancestral adaptations to appropriate stimuli 
consciousness, or the mind-element, is wholly absent ; we 
can only say that this element, if present, reveals no 
evidence of the fact. But, on the other hand, if a lowly 
organised animal does learn by its own individual experi- 
ence, we are in possession of the best available evidence 
of conscious memory leading to intentional adaptation. 
Therefore our criterion applies to the upper limit of non- 
mental action, not to the lower limit of mental. 
Of course to the sceptic this criterion may appear un- 
satisfactory, since it depends, not on direct knowledge, 
but on inference. Here, however, it seems enough to 
point out, as already observed, that it is the best 
criterion available ; and further, that scepticism of this 
kind is logically bound to deny evidence of mind, not only 
in the case of the lower animals, but also in that of the 
