XLVIII. Again, of justice there are three species. For there is one kind which is conversant with the gods; a second which has reference to men; and a third, which concerns the dead. For they who sacrifice according to the laws, and who pay due respect to the temples, are manifestly pious to the gods. And those who repay what has been lent to them, and restore what has been deposited with them, act justly as to men. And those who pay due respect to the tombs, clearly are pious towards the dead. There is, therefore, one justice towards the Gods, a second towards men, and a third towards the dead. XLIX. In the same way, there are also three species of knowledge. There is one kind which is practical, a second which is productive, a third which is theoretical. For the science of building houses or ships, is production. For one can see the work which is produced by it. Political science, and the science of playing the flute, or the harp, or such things as that, is practical; for one cannot see any visible result which has been produced by them, and yet they are doing something. For one man plays the flute or plays the harp, and another occupies himself with state affairs. Again, geometrical, and harmonic, and astronomical science are all theoretical, for they do nothing, and produce nothing. But the geometrician theorizes as to what relation lines bear to one another; and the harmonist speculates about sounds, and the astronomer about stars and about the world. Accordingly, of sciences some are theoretical, others productive, and a third species is practical. L. Of medical science there are five species: one, pharmaceutical; a second, manual; a third, conversant about the regulation of the manner of life, and the diet; a fourth, the business of which is to detect diseases; and the fifth is remedial. The pharmaceutical relieves infirmities by means of medicines; the manual heals men by cutting and cauterizing; the one which attends to the diet, gets rid of diseases by altering and regulating the diet; the fourth produces its effects by a thorough comprehension of the nature of the disease; and the last relieves men from suffering by bringing prompt assistance at the moment. Medical science, then, is divided into the pharmaceutical, the manual, the dietetic, the diagnostic, and the remedial. LI. Of law there are two divisions. For there is a written and an unwritten law. The one by which we regulate our constitutions in our cities, is the written law; that which arises from custom, is the unwritten law. As, for instance, for a man to come naked into the market place, or to wear woman’s clothes, are actions which are not prohibited by any law, and yet we never do them because they are forbidden by the unwritten law. Law, therefore, is divided into the written and the unwritten law.