Godwin and his adherents could reply that one of the checks on over-population is prudential restraint, which Malthus himself recognised, and that this would come more extensively into operation with that progress of enlightenment which their theory assumed. [Footnote: This is urged by Hazlitt in his criticism of Malthus in the Spirit of the Age.] But the criticisms of Malthus dealt a trenchant blow to the doctrine that human reason, acting through legislation and government, has a virtually indefinite power of modifying the condition of society. The difficulty, which he stated so vividly and definitely, was well calculated to discredit the doctrine, and to suggest that the development of society could be modified by the conscious efforts of man only within restricted limits. [Footnote: The recent conclusions of Mr. Knibbs, statistician to the Commonwealth of Australia, in vol. i. of his Appendix to the Census of the Commonwealth, have an interest in this connection. I quote from an article in the Times of August 5, 1918: "An eminent geographer, the late Mr. E. G. Ravenstein, some years ago, when the population of the earth was estimated at 1400 million, foretold that about the middle of this century population would have reached a limit beyond which increase would be disastrous. Mr. Knibbs is not so pessimistic and is much more precise; though he defers the disastrous culmination, he has no doubt as to its inevitability. The limits of human expansion, he assures us, are much nearer than popular opinion imagines; the difficulty of food supplies will soon be most grave; the exhaustion of sources of energy necessary for any notable increase of population, or advance in the standards of living, or both combined, is perilously near. The present rate of increase in the world's population cannot continue for four centuries."] 6. The Essay of Malthus afterwards became one of the sacred books of the Utilitarian sect, and it is interesting to notice what Bentham himself thought of perfectibility. Referring to the optimistic views of Chastellux and Priestley on progressive amelioration he observed that "these glorious expectations remind us of the golden age of poetry." For perfect happiness "belongs to the imaginary region of philosophy and must be classed with the universal elixir and the philosopher's stone." There will always be jealousies through the unequal gifts of nature and of fortune; interests will never cease to clash and hatred to ensue; "painful labour, daily subjection, a condition nearly allied to indigence, will always be the lot of numbers"; in art and poetry the sources of novelty will probably be exhausted. But Bentham was far from being a pessimist. Though he believes that "we shall never make this world the abode of happiness," he asserts that it may be made a most delightful garden "compared with the savage forest in which men so long have wandered." [Footnote: Works, vol. i. p. 193 seq.] 7.