234 THE INTELLIGENCE OF MAMMALS 
involved in most animal performances is a matter of much 
difficulty. We may be guided on the one hand by analogy 
with ourselves, which leads us to infer that actions similar 
to our own are accompanied by similar mental states; and 
by the law of parsimony on the other, which forbids us to 
assume the existence of higher mental qualities if the phe- 
nomena can be explained in terms of simpler mental pro- 
cesses. In the imperfect state of our knowledge these two 
guides often lead to opposed conclusions. If we applied the 
principle of Morgan to the psychology of our fellow human 
beings we should be continually led astray. So in our inter- 
pretations of the psychology of the higher animals we may 
very frequently be “missing it” more or less widely in our 
adherence to this principle. The antecedent probability 
in favor of not giving the animal the benefit of the doubt 
diminishes as we ascend the scale of psychic life. We may 
suspect that our interpretations “fall short,’’ but our opin- 
ions cannot be said to rest on a secure basis until we are 
able to support them by experimental proof. The principle 
of Morgan affords a check to the natural tendency to “an- 
thropomorphism” which is a common human failing; it 
throws the burden of proof on whomsoever attempts to es- 
tablish the existence in animals of higher faculties, and if 
the positive conclusions to which it permits us to come fall 
short of the truth we can at least rely on them so far as 
they go. 
As a typical instance of the workings of the animal mind 
we may cite the performances of Professor Lloyd Morgan’s 
dog, Toby, which had learned how to open a gate that led 
out of his master’s.yard. The gate was fastened by a latch, 
but swung open by itself if the latch was raised. Whenever 
the dog desired to make his escape he put his head between 
the bars, lifted the latch and went out. Such an act might 
