Having completed his exposition of things, the author now proceeds to discuss the subject of signs. He first defines what a sign is, and shows that there are two classes of signs, the natural and the conventional. Of conventional signs (which are the only class here noticed), words are the most numerous and important, and are those with which the interpreter of Scripture is chiefly concerned. The difficulties and obscurities of Scripture spring chiefly from two sources, unknown and ambiguous signs. The present book deals only with unknown signs, the ambiguities of language being reserved for treatment in the next book. The difficulty arising from ignorance of signs is to be removed by learning the Greek and Hebrew languages, in which Scripture is written, by comparing the various translations, and by attending to the context. In the interpretation of figurative expressions, knowledge of things is as necessary as knowledge of words; and the various sciences and arts of the heathen, so far as they are true and useful, may be turned to account in removing our ignorance of signs, whether these be direct or figurative. Whilst exposing the folly and futility of many heathen superstitions and practices, the author points out how all that is sound and useful in their science and philosophy may be turned to a Christian use. And in conclusion, he shows the spirit in which it behoves us to address ourselves to the study and interpretation of the sacred books.