In proportion to the size of its body, a dolphin’s brain is smaller than the human brain but larger than the great apes. Because dolphins do have relatively large brains, researchers are particularly interested in how well they communicate.

In the wild, dolphins use two kinds of sounds for communication: clicks, which they use to probe the sea and “see” their environment; and whistles， which they use in dolphin-to-dolphin communication, probably to express emotional states and identify the animals to the group. However, there is little evidence that dolphins in the wild use symbols or apply any rules of grammar in their normal communications.

In testing the ability of dolphins to communicate, psychologist Louis Herman has been training dolphins to respond to hand signals or whistles. So far, he has taught two dolphins to respond to approximately 50 such signals.

For example, in the top-right photo, Herman is raising his hands, which is part of a signal for “person over”, which means “jump over the person in the pool.”

The bottom-right photo shows the dolphin carrying out the command by jumping over the person and not the surfboard.

Herman found that dolphins can understand a variety of hand signals and perform behaviors in sequence. For example, the hand signal combination, “basket, right, Frisbee, fetch”, means “Go to the Frisbee on the right and take it to the basket.” Although Herman admits that the ability of dolphins to acquire the four rules of language is much inferior to that of humans, he insists that dolphins understand word order and can grasp concepts, such as the hoop (no matter if it is round, octagonal, or square). Thus, he argues that dolphins do have some understanding of grammar of syntax.

Some researchers reply that what may look like language in dolphins may simply be imitation, mimicry, or rote learning, which is observed in many pets. Thus, although dolphins understand a variety of signals, perform behaviors in sequence, and form concepts, they show minimal evidence of using abstract symbols to communicate or applying rules of grammar to generate meaningful sentences. It is these two criteria that distinguished the ability to use language from the simple ability to communicate with signs, sounds or gestures.