178 BEGINNINGS OF INTELLIGENCE 
latter reinforces the first reaction. The pleasure-pain 
response then resolves itself into the formation of associa- 
tions. Withdrawing and defensive responses are usually 
initiated by pain giving stimuli, and the instinctive or 
random movement which brings a painful stimulus is in- 
hibited under similar conditions in the future, not because 
of the pain or its physiological correlate, but because it 
comes to be associated with a withdrawing or defensive, 
and hence an incongruous or inhibitory reaction. Pleasure 
and pain thus interpreted have no mysterious power of 
stamping in or stamping out certainassociations. Whether 
the result is reinforcement or inhibition depends on the 
way in which a reaction and the secondary responses re- 
sulting from the situation in which the organism is thereby 
brought, happen to harmonize. 
The step from instinct to intelligence viewed as a physio- 
logical process involves, therefore, no essentially new 
element beyond the well known physiological properties of 
the nervous system, and we are not committed to any par- 
ticular hypothesis as to the physiological accompaniments 
of pleasure and pain, or pleasantness and unpleasantness, 
in order to understand how behavior may become adaptively 
modified. How far the interpretation given will enable us 
to explain the development of intelligence I do not pretend 
to say. It may break down in attempts to apply it to 
higher forms of learning, but it affords a useful working 
hypothesis and takes us a way, I think, toward the solution 
of our problem. 
BIBLIOGRAPHY 
Barn, A. The Sensations and the Intellect, 3d. ed., 94. 
The Emotions and the Will, 4th. ed., ’99. 
Batpwin, J. M. Mental Development in the Child and in the Race. 
Methods and Processes, 2nd. ed., N. Y., 797. 
Development and Evolution, N. Y., ’02. 
