ANIMAL INTELLIGENCE, AND HOW TO STUDY IT 9 
make a special study of mind—the psychologists— 
and perhaps the biologists might be added, there is 
considerable diversity of opinion as to the exact nature 
of animal intelligence. One very distinguished writer 
would deny the power of thought proper to any creature 
that did not use language—articulate words. He 
would even go so far as to affirm that man himself can 
only think in words. But plainly his definition of 
“thinking” must be very restricted ; it must be con- 
fined to a very few mental processes, and leave out a 
vast amount of what enters into the daily mental being 
of every man. There are others that would not go 
so far as this writer, who, nevertheless, deny to animals 
the power to perceive relations and to reason. When 
a dog appears to act as if he had reasoned, those who 
hold such views would explain by admitting that the 
animal had profited by experience ; they would concede 
that he was intelligent, but claim that his apparently 
rational action was merely the outcome of mental 
association, or a use of “ sense-experience.” When, for 
example, a dog or a cat opens a door by manipulating 
the latch, writers of this school deny reasoning or any 
analogous processes, but explain the action by utilisa- 
tion of sense-experience under the law of association. 
The dog somehow on one occasion, more or less accident- 
ally, opened the door by using his paws or teeth on the 
latch, and this at once established an association in 
sense-experience ; hence any future repetitions have 
nothing to do with any process of reasoning to the 
effect that if the paw be used on the latch the door 
will open. On the contrary, such writers deny the 
power to the animal to perceive any such relations. 
This theory reduces the mental life of the animal 
very considerably, and restricts the dog’s thoughts 
within a narrow compass. But is there not a danger 
of cutting down the possibilities of animal intelligence 
