4 INTRODUCTION 
we could never feel much confidence in any conclusions as 
to the kind of conscious states which make up their mental 
life. We may be asked, in what way do we know these 
animals have conscious states at all? May they not be as 
Descartes has considered all animals below man, merely 
unconscious automata? The question throws us back upon 
what criterion we adopt of consciousness and upon this 
subject the opinions of psychologists present us with no end 
of differences. 
The criterion of consciousness which is perhaps most 
widely adopted at the present time is the ability to learn by 
experience, or associative memory. Among those who have 
adopted this standpoint may be mentioned Bethe, Loeb 
and Bohn. Romanes and Lloyd Morgan, while they 
recognize that ability to learn is indicative of the presence of 
consciousness, hesitate to draw the conclusion that con- 
sciousness is absent in those animals which are devoid of 
associative memory. In his work on Animal Intelligence 
Romanes states that “because a lowly organized 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.” 
Lloyd Morgan writes likewise in a guarded manner: “ When 
we see that a chick, for example, pecks at first at any small 
object, it is difficult to say, on these grounds, whether it is 
a sentient animal or an unconscious automaton; and if it 
continued to behave in a similar fashion througout life, 
our difficulty would still remain. But when we see that 
some objects are rejected while others are selected, we infer 
that consciousness in some way guides its behavior. The 
chick has profited by experience. But even this is only 
