The term "darkness" in this case is metaphorical, and borrowed from that which is natural. What natural darkness is, and wherein it consists, all men know; if they know it not in its cause and reason, yet they know it by its effects. They know it is that which hinders men from all regular operations which are to be guided by the outward senses. And it is twofold:— 1. When men have not light to see by, or when the usual light, the only external medium for the discovery of distant objects, is taken from them. So was it with the Egyptians during the three days' darkness that was on their land. They could not see for want of light; they had their visive faculty continued unto them, yet having "no light," they "saw not one another, neither arose any from his place," Exod.10:23