He did not idealize the constitutions of the olden times. Since all men then carried daggers, the presumption, he says, is that they needed them and used them. Since conditions where violence reigned must have continued indefinitely, if political change had been prohibited, he finds it good as well as inevitable that laws be modified from time to time. The permanency of those of Sparta is worthy of high praise; but he traces the corruption and decay of the Spartan state to failure to make needed reforms. In general he strikes a much more just balance between Spartan and Athenian achievement than does Plato. The first test he applies to institutions, such as the family and the state, is their naturalness--their source in the nature of man as that is revealed in his history. He was well aware that a political science that was based upon _perfected_ human nature was, indeed, suited only for "gods and sons of gods"; that the only principles of government which had real value were those which had approved themselves in practice. "All discoveries," he says,[55] "have been already made, although in some cases they have not been combined, and in others, when made, are not acted upon." "The _Politics_ of Aristotle," says a recent writer, "is the one great book on the science of government because it is the only one which is wholly empirical." That is too high praise. For the _Politics_ of Aristotle differs from the _Prince_ of Machiavelli in other respects, of course, but noticeably in that the Greek has moral ideals, the Italian none. With Aristotle, as with Plato, the state has an ethical purpose. He requires it to justify not only its acts but its existence. Iniquitous governments might exist,--Aristotle's world was full of them, in fact,--and his mind was too curious of all things political for him to leave them out of his observation: he has, indeed, considered minutely the ways and means for the preservation of all kinds of states, and has shown therein that he had as keen an eye for the realities as had Machiavelli himself. But he would never have permitted, much less advised, his legislator to use foul means to establish a just government or fair means to establish an unjust one.