The perplexity of medicine is paralleled by the perplexity of law; in which, again, Plato would have men follow the golden rule of simplicity. Greater matters are to be determined by the legislator or by the oracle of Delphi, lesser matters are to be left to the temporary regulation of the citizens themselves. Plato is aware that laissez faire is an important element of government. The diseases of a State are like the heads of a hydra; they multiply when they are cut off. The true remedy for them is not extirpation but prevention. And the way to prevent them is to take care of education, and education will take care of all the rest. So in modern times men have often felt that the only political measure worth having—the only one which would produce any certain or lasting effect, was a measure of national education. And in our own more than in any previous age the necessity has been recognized of restoring the ever-increasing confusion of law to simplicity and common sense. When the training in music and gymnastic is completed, there follows the first stage of active and public life. But soon education is to begin again from a new point of view. In the interval between the Fourth and Seventh Books we have discussed the nature of knowledge, and have thence been led to form a higher conception of what was required of us. For true knowledge, according to Plato, is of abstractions, and has to do, not with particulars or individuals, but with universals only; not with the beauties of poetry, but with the ideas of philosophy. And the great aim of education is the cultivation of the habit of abstraction. This is to be acquired through the study of the mathematical sciences. They alone are capable of giving ideas of relation, and of arousing the dormant energies of thought.