Of all the instincts, two groups or classes stand out from the rest: the responses to organic needs, and the responses to other persons. The first class includes eating, avoiding injury, and many others; the second class includes the herd instinct, the mating instinct and the parental instinct, these three and perhaps no others.{139}

These two groups out, the rest are rather a miscellaneous collection, including the "random" or playful activity of young children, locomotion, vocalization, laughter, curiosity, rivalry and fighting. They might be named the "non-specific instincts", because the stimulus for each is not easy to specify, being sometimes another person, so that this group has great social importance, but sometimes being impersonal. This third class might also be called the "play instincts", since they are less essential than the other classes for maintaining the individual life or for propagating the species; and are, we may say, less concerned with the struggle for existence than with the joy of living.

Our classification then has three heads:

(1) Responses to organic needs,
(2) Responses to other persons,
(3) Play responses.