Since the Enlightenment is usually regarded as something that happened rather more in France than anywhere else, this is perhaps the best place to ask what it was, even if the question can only be answered in the vaguest of terms. It was not some kind of a torch, kindled by Bacon, blown into flame by Newton and Locke and thence passed to the outstretched hands of the French philosophes. If it had anything to do with light, it was more like the green band in the rainbow, which began mostly as blue and ended up unmistakably yellow. Some such way of looking at things at least serves as a reminder that the movement was in a state of continual change, but it remains such a crude oversimplification that it may be more of a hindrance than a help, for the Enlightenment was less a body of doctrine than a number of shared premises from which men of different temperaments, placed in different situations, drew quite radically different conclusions.

The Enlightenment implied a simultaneous commitment to three assumptions, which had not been generally believed or taken for granted before the latter part of the seventeenth century, and which were to appear increasingly implausible in the nineteenth. The first of these was that Nature was a self-regulating system of laws.