The introductory remarks of the Differentiae are worth translating, since they reveal one of the most marked characteristics of Isidore’s thinking, the stress that he laid on words. They are as follows:
Many of the ancients sought to define the differences of words, making some subtle distinction between word and word. But the heathen poets disregarded the proper meanings of words under the compulsion of metre. And so, beginning with them, it became the custom for writers to use words without proper discrimination. But although words seem alike, still they are distinguished from one another by having each an origin of its own.[26] Cato was the first of the Latins to write on this subject,[27] after whose example I have in part written myself of a very few, and have in part taken them from the books of the writers.[28]
The De Natura Rerum[29] is a work of great importance for an understanding of Isidore’s view of the physical universe. The preface is of especial interest as giving some hints of his methods of literary work and of his attitude toward pagan writers. It is addressed to Sisebutus, who was king of the Visigoths from 612 to 620.[30] It runs as follows:
Although, as I know, you excel in talent and eloquence and in the varied accomplishments of literature (vario flore literarum), you are still anxious for greater attainment, and you ask me to explain to you something of the nature and causes of things. I, on my part, have run over the works of earlier writers, and am not slow to satisfy your interest and desire, describing in part the system of the days and months; the goals of the year, as well, and the changes of the seasons; the nature also of the elements; the courses of the sun and moon, and the significance of certain stars;[31] the signs of the weather, too, and of the winds; and besides, the situation of the earth, and the alternate tides of the sea. And setting forth all things as they are written by the ancients, and especially in the works of catholic writers, we have described them briefly. For to know the nature of these things is not the wisdom of superstition, if only they are considered with sound and sober learning. Nay, if they were in every way far removed from the search for the truth, that wise king would by no means have said: “Ipse mihi dedit horum quae sunt scientiam veram ut sciam dispositionem coeli et virtutes elementorum, conversionum mutationes, et divisiones temporum, annorum cursus et stellarum dispositiones.”
Wherefore, beginning with the day, whose creation appears first in the order of visible things, let us expound those remaining matters as to which we know that certain men of the heathen and of the church have opinions, setting down in some cases both their thoughts and words, in order that the authority of the very words may carry belief.
The general organization of the matter treated by Isidore in the De Natura Rerum is worth noticing. The preface quoted above indicates that the order of treatment is to follow the order of creation. The first topic, therefore, suggested by the creation of light, we should expect to be the phenomenon of light. Instead of this it is the day, in the calendar sense, that is described, with the natural sequel of the week, month, and year as collections of days. This section really constitutes a brief account of the elements of chronology. Next created are the heavens; so we have next astronomy, presented in a condensed form, to which are appended a few chapters on meteorological matters, such as thunder, clouds, the rainbow, wind, and finally pestilence, which comes in appropriately here as being “a corruption of the air”. The topic next in order, following the first chapter of Genesis, is the sea; and after that, the dry land. It should be noted that this view of the physical universe according to the order of its creation, corresponds roughly to the analysis of matter into the four elements, fire, air, water, earth. As will be shown later, such correspondences are an important factor in the intellectual outlook of the time. This was the kind of mental connection with which people were familiar.[32]
The Liber Numerorum contains nothing arithmetical in the modern sense of the word, in spite of Braulio’s statement that in it Isidore “touched on the science of arithmetic”.[33] Its fuller title is “The book of the numbers which occur in the Holy Scriptures”, and the body of the book is taken up with the mystic significance of each number from one to twenty, omitting seventeen, and also of twenty-four, thirty, forty, forty-six, fifty, and sixty. The method of treatment indicates an advanced mysticism of numbers. The book is not so much an attempt to show the significance of numbers occurring in particular connections, as it is a generalized guide to their mystical interpretation, laying down rules to govern the interpretation of each number, no matter where it occurs. It should be remarked that this was really “the science of number” of the dark ages, and that Braulio’s use of the term “arithmetic” as applying to it was in accordance with the best usage of the time.[34]
The Allegoriae is of a character similar to the Liber Numerorum. It contains in brief form the principal allegories which were read into the books of the Old and the New Testaments, and is evidently meant to constitute a sort of reference book for Scriptural allegory. It possesses little interest.
One of the most important of the writings of Isidore is the Sententiae, in three books. It is a systematic treatise on Christian doctrine and morals,[35] and is culled chiefly from the Moralia of Gregory the Great. As might be guessed from its source, it is not a work of an enlightened character. However, while it is largely taken up with the technicalities of Christian thinking, it is frequently valuable as affording fuller and more specific statements on some matters of interest than are found elsewhere in Isidore’s works. Isidore and Gregory were in substantial agreement in their attitude toward life, but there are indications that in some respects Isidore was not quite as thorough-going as his model.[36]
Among Christian scholars from the beginning there had been a desire to bring the traditional ideas of pagan cosmography into subordination to the Christian scheme. This impulse was strongly, though blindly, felt by Isidore, and it led to his several attempts at a comprehensive account of the universe. Perhaps the most interesting of these is the De Ordine Creaturarum, which differs from the others by including the spiritual as well as the material universe. The difference did not make for rationality, and in this short work Isidore is seen at his scientific worst. As in the De Natura Rerum, the dominating factors in the description of the physical universe are the first chapter of Genesis and the theory of the four elements.