This is seen most familiarly in the use of metaphors. Thus, in an Oxford satire, which deservedly made a sensation in its day, it is said that Vice “from its hardness takes a polish too.”(1) Whence we might argue, that, whereas Caliban was vicious, he was therefore polished; but politeness and Caliban are incompatible notions. Or again, when some one said, perhaps to Dr. Johnson, that a certain writer (say Hume) was a clear thinker, he made answer, “All shallows are clear.” But supposing Hume to be in fact both a clear and a deep thinker, yet supposing clearness and depth are incompatible in their literal sense, which the objection seems to imply, and still in their full literal sense were to be ascribed to Hume, then our reasoning about his intellect has ended in the mystery, “Deep Hume is shallow;” whereas the contradiction lies, not in the reasoning, but in the fancying that inadequate notions can be taken as the exact representations of things. Hence in science we sometimes use a definition or a _formula_, not as exact, but as being sufficient for our purpose, for working out certain conclusions, for a practical approximation, the error being small, till a certain point is reached. This is what in theological investigations I should call an economy. A like contrast between notions and the things which they represent is the principle of suspense and curiosity in those enigmatical sayings which were frequent in the early stage of human society. In them the problem proposed to the acuteness of the hearers, is to find some real thing which may unite in itself certain conflicting notions which in the question are attributed to it: “Out of the eater came forth meat, and out of the strong came forth sweetness;” or, “What creature is that, which in the morning goes on four legs, at noon on two, and on three in the evening?” The answer, which names the thing, interprets and thereby limits the notions under which it has been represented.