One of the things that distinguish man from the animals is the power of speech. While it is true that most animals and birds cannot take cries which indicates emotion, anger, fear, affection nevertheless. Their range of sounds is very limited so that they are not capable of expressing more complicated emotions. On the other hand, man can express a very wide range of ideas and emotions through speech. Words are only symbols to which special values and meanings have become attached by general agreements. The same objects consisting of printed pages and the cover is called by a French speaker, Libra. By an English speaker, Book. And by a Hindi speaker, Kitab. The object is the same in each case. But in each linguistic community a different word to describe it has been agreed upon. Other symbols may be used instead of linguistic ones. A red light is used to indicate danger. A policeman's up held hand tells us to stop. A forefinger held to the lips wants us to be quiet but these substitutes are fairly few in number and therefore cannot be used except in very limited circumstances.