A knowledge of degrees is like a key for opening the causes of things, and for entering into them. Without that knowledge, scarcely anything of cause can be known. For without it, the objects and subjects of both worlds appear so simple as though there were nothing in them beyond that which meets the eye, when yet the things that appear are as one to thousands, indeed, to myriads, compared with the things which lie hidden within. The interiors which do not lie open can by no means be disclosed except by a knowledge of degrees. For exterior things go on to interior things, and through these to inmost things by means of degrees, not by continuous degrees but by discrete degrees. Continuous degrees are defined as lessenings or decreasings from grosser to finer, or from denser to rarer; or rather as growths and increasings from finer to grosser, or from rarer to denser, exactly like gradations of light to shade, or of heat to cold. Discrete degrees, however, are quite different. They are like things prior, posterior and final, and like end, cause and effect. These degrees are called discrete, because the prior is by itself, the posterior by itself and the final by itself, but yet taken together they make one. The atmospheres from highest to lowest, or from the sun to the earth and which are called ethers and airs, are separated into such degrees. They are like simple things, collections of those, and again collections of these which taken together are called a composite. These degrees are discrete because they exist distinctly and these are understood as degrees of height, whereas the former degrees are continuous because they increase continuously, and these are understood as degrees of breadth.