Front Page Titles (by Subject) The Doctrine of Population. - The Theory of Political Economy
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The Doctrine of Population. - William Stanley Jevons, The Theory of Political Economy 
The Theory of Political Economy (London: Macmillan, 1888) 3rd ed.
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The Doctrine of Population.
IT is no part of my purpose in this work to attempt to trace out, with any approach to completeness, the results of the theory given in the preceding chapters. When the views of the nature of Value, and the general method of treating the subject by the application of the fluxional calculus, have received some recognition and acceptance, it will be time to think of results. I shall therefore only occupy a few more pages in pointing out the branches of economic doctrine which have been passed over, and in indicating their connection with the theory.
The doctrine of population has been conspicuously absent, not because I doubt in the least its truth and vast importance, but because it forms no part of the direct problem of Economics. I do not remember to have seen it remarked that it is an inversion of the problem to treat labour as a varying quantity, when we originally start with labour as the first element of production, and aim at the most economical employment of that labour. The problem of Economics may, as it seems to me, be stated thus:—Given, a certain population, with various needs and powers of production, in possession of certain lands and other sources of material: required, the mode of employing their labour which will maximise the utility of the produce. It is what mathematicians would call a change of the variable, afterwards to treat that labour as variable which was originally a fixed quantity. It really amounts to altering the conditions of the problem so as to create at each change a new problem. The same results, however, would generally be obtained by supposing the other conditions to vary. Given, a certain population, we may imagine the land and capital at their disposal to be greater or less, and may then trace out the results which will, in many respects, be applicable respectively to a less or greater population with the original land and capital.