The problem of dark ages, which an advocate of Progress must explain, was waved away by Priestley in his Lectures on History with the observation that they help the subsequent advance of knowledge by “breaking the progress of authority.” [Footnote:  This was doubtless suggested to him by some remarks of Hume in The Rise of Arts and Sciences.] This is not much of a plea for such periods viewed as machinery in a Providential plan.  The great history of the Middle Ages, which in the words of its author describes “the triumph of barbarism and religion,” had been completed before Priestley’s Lectures appeared, and it is remarkable that he takes no account of it, though it might seem to be a work with which a theory of Progress must come to terms.

Yet the sceptical historian of the Decline and Fall of the Roman Empire, who was more at home in French literature than any of his fellow-countrymen, was not opposed to the theory of Progress, and he even states it in a moderate form.  Having given reasons for believing that civilised society will never again be threatened by such an irruption of barbarians as that which oppressed the arms and institutions of Rome, he allows us to “acquiesce in the pleasing conclusion that every age of the world has increased, and still increases, the real wealth, the happiness, the knowledge and perhaps the virtue of the human race.”

“The discoveries of ancient and modern navigators, and the domestic history or tradition of the most enlightened nations, represent the human savage, naked both in mind and body, and destitute of laws, of arts, of ideas, and almost of language.  From this abject condition, perhaps the primitive and universal state of man, he has gradually arisen to command the animals, to fertilise the earth, to traverse the ocean, and to measure the heavens.  His progress in the improvement and exercise of his mental and corporeal faculties has been irregular and various, infinitely slow in the beginning, and increasing by degrees with redoubled velocity; ages of laborious ascent have been followed by a moment of rapid downfall; and the several climates of the globe have felt the vicissitudes of light and darkness.  Yet the experience of four thousand years should enlarge our hopes and diminish our apprehensions; we cannot determine to what height the human species may aspire in their advances towards perfection; but it may safely be presumed that no people, unless the face of nature is changed, will relapse into their original barbarism.” [Footnote:  Decline and Fall of the Roman Empire, ch. xxxviii. ad fin.]

But Gibbon treats the whole subject as a speculation, and he treats it without reference to any of the general principles on which French thinkers had based their theory.  He admits that his reasons for holding that civilisation is secure against a barbarous cataclysm may be considered fallacious; and he also contemplates the eventuality that the fabric of sciences and arts, trade and manufacture, law and policy, might be “decayed by time.”  If so, the growth of civilisation would have to begin again, but not ab initio.  For “the more useful or at least more necessary arts,” which do not require superior talents or national subordination for their exercise, and which war, commerce, and religious zeal have spread among the savages of the world, would certainly survive.