He cannot disentangle the arts from the virtues--at least he is always arguing from one to the other.
His notion of music is transferred from harmony of sounds to harmony of life: in this he is assisted by the ambiguities of language as well as by the prevalence of Pythagorean notions.

And having once assimilated the state to the individual, he imagines that he will find the succession of states paralleled in the lives of individuals.
Still, through this fallacious medium, a real enlargement of ideas is attained.

When the virtues as yet presented no distinct conception to the mind, a great advance was made by the comparison of them with the arts; for virtue is partly art, and has an outward form as well as an inward principle.

The harmony of music affords a lively image of the harmonies of the world and of human life, and may be regarded as a splendid illustration which was naturally mistaken for a real analogy.
In the same way the identification of ethics with politics has a tendency to give definiteness to ethics, and also to elevate and ennoble men's notions of the aims of government and of the duties of citizens; for ethics from one point of view may be conceived as an idealized law and politics; and politics, as ethics reduced to the conditions of human society.

There have been evils which have arisen out of the attempt to identify them, and this has led to the separation or antagonism of them, which has been introduced by modern political writers.