It is language, more obviously than any thing else, that distinguishes man from the rest of the animal world. At one time it was common to define a man as a th inking animal, but we can hardly imagine thought without words- not thought that is at all precise, anyway. More recently, man has often been described as a tool- making animal; but language itself is the most remarkable tool that a man has invented, and is the one that makes all the others possible. The most primitive tools, admittedly, may have come earlier than language: the higher apes use sticks sometimes for digging, and gave even been observed to break sticks for this purpose. But tools of any greater sophistication demand the kind of human co-operation and division of labour which is hardly possible without language. Language, in fact, is the great machine tool which makes human culture possible.
Other animals, it is true, communicate with one another, or at any rate stimulate one another to action, by means of cries. Many birds utter warning calls at the approach of danger; some animals have mating calls; apes utter different cries expressive of anger, fear, pleasure. But these various means of communication differ in important ways from human language. Animals’ cries are not articulate. This means, basically, that they lack structure. They lack, for example, the kind of structure given by the contrast between vowels and consonants. They also the lack of the kind of the structure that enables us to divide a human utterance into words. We can change an utterance by replacing one word in it by another: a sentry can say ‘Tanks approaching from the north’ or ‘Tanks approaching from the west’ ; but a bird has a single indivisible alarm cry, which means ‘Danger!’ This is why the number of signals that the animal can make is very limited : The Great Tim has about 20 different calls, whereas in human language the number of possible utterance is infinite. It also explains why animal cries are very general in meaning. These differences will become clearer if we consider some of the characteristics of human language.