Knowledge is employed in the service of the necessity of life and primarily in the service of the instinct of personal preservation. The necessity and this instinct have created in man the organs of knowledge and given them such capacity as they possess. Man sees, hears, touches, tastes and smells that which it is necessary for him to see, hear, touch, taste and smell in order to preserve his life. The decay or loss of any of these senses increases the risks with which his life is environed, and if it increases them less in the state of society in which we are actually living, the reason is that some see, hear, touch, taste and smell for others. A blind man, by himself and without a guide, could not live long. Society is an additional sense; it is the true common sense.

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