But free trade presents itself to us, among its more recent supporters, in a very different aspect--the free traders, abandoning metaphysical postulates, assert two theses of practical importance: (_a_) that of an _economic hedonistic maximum_, which they suppose identical with the maximum of social desirability;[55] and (_b_) the other, that this hedonistic maximum can only be completely secured by means of the fullest economic liberty. These two theses certainly take us outside metaphysics and into the region of reality; but not actually into the region of science. Indeed the first of them contains a statement of the ends of social life, which may perhaps be welcome, but is not a deduction from any scientific proposition. The second thesis cannot be proved except by reference to experience, _i.e._ to what we know of human psychology, and to what, by approximate calculation, we may suppose that psychology will still probably be in the future. A calculation which can be made, and has been made with great acumen, with great erudition and with great caution and which hence may even be called scientific, but only in a metaphorical and hyperbolical sense, as we have already remarked: hence the knowledge which it affords us, can never have the value of strictly scientific knowledge.[56] Pareto, who is both one of the most intelligent and also one of the most trustworthy and sincere, of the recent exponents and supporters of free trade,[57] does not deny the limited and approximate nature of its conclusions; which appears to him so much the more clearly in that he uses mathematical formulae, which show at once the degree of certainty to which statements of this kind may lay claim.