The difficulty presented by periods of decadence and barbarism succeeding epochs of enlightenment is met by the assertion that in such dark times the world has not stood still; there has really been a progression which, though relatively inconspicuous, is not unimportant. In the Middle Ages, which are the prominent case, there were improvements in mechanical arts, in commerce, in some of the habits of civil life, all of which helped to prepare the way for happier times. Here Turgot's view of history is sharply opposed to Voltaire's. He considers Christianity to have been a powerful agent of civilisation, not a hinderer or an enemy. Had he executed his design, his work might well have furnished a notable makeweight to the view held by Voltaire, and afterwards more judicially developed by Gibbon, that "the triumph of barbarism and religion" was a calamity for the world. Turgot also propounded two laws of development. He observed that when a people is progressing, every step it takes causes an acceleration in the rate of progress. And he anticipated Comte's famous "law" of the three stages of intellectual evolution, though without giving it the extensive and fundamental significance which Comte claimed for it. "Before man understood the causal connection of physical phenomena, nothing was so natural as to suppose they were produced by intelligent beings, invisible and resembling ourselves; for what else would they have resembled?" That is Comte's theological stage. "When philosophers recognised the absurdity of the fables about the gods, but had not yet gained an insight into natural history, they thought to explain the causes of phenomena by abstract expressions such as essences and faculties." That is the metaphysical stage. "It was only at a later period, that by observing the reciprocal mechanical action of bodies hypotheses were formed which could be developed by mathematics and verified by experience." There is the positive stage. The observation assuredly does not possess the far-reaching importance which Comte attached to it; but whatever value it has, Turgot deserves the credit of having been the first to state it.