That one of Isidore’s books which is of by far the greatest importance for an understanding of the secular thought of the day, is the Etymologies. This is a sort of dictionary or encyclopedia of all knowledge.[37] As Braulio puts it, it contained “about all that ought to be known”, and it may be taken as representing the widest possible scope of secular knowledge that an orthodox Spaniard of the dark ages could allow himself. Indeed, so hospitable an attitude toward profane learning as Isidore displayed was unparalleled in his own period, and was never surpassed throughout the middle ages.

The encyclopedic character of the Etymologies may best be realized by a general view of its contents. The titles of the twenty books into which it is divided are as follows:

Etymologiarum Libri XX.

To the modern reader, familiar with the names of only the modern sciences, this series of titles, which includes an almost complete list of the ancient sciences, may not be very illuminating. For this reason it is perhaps allowable to translate them, where it is possible to do so, into their modern equivalents. Thus we have grammar (Bk. 1), rhetoric and logic (Bk. 2), arithmetic, geometry, music, astronomy (Bk. 3), medicine (Bk. 4), law and chronology (Bk. 5), theology (Bks. 6–8), human anatomy and physiology (Bk. 11), zoölogy (Bk. 12), cosmography and physical geography (Bks. 13–14), architecture and surveying (Bk. 15 and part of Bk. 19), mineralogy (Bk. 16), agriculture (Bk. 17), military science (Bk. 18). This partial enumeration of the subjects treated in Isidore’s Etymologies forms an imposing array, and serves to explain something of the importance of the work in the history of thought.

The secret of this inclusiveness lay, however, not in an expanded, but in a contracted interest. Although Isidore is not surpassed in comprehensiveness by any one of the line of Roman encyclopedists who preceded him, in the quality of his thought and the extent of his information he is inferior to them all. Secular knowledge had suffered so much from attrition and decay that it could now be summarized in its entirety by one man.

In spite of this it is very clear that if Isidore had treated these topics with any degree of reference to the actual realities of his own time, he would have left us a work of inestimable value. But he did not do so; he drew, not upon life, but upon books for his ideas; there was no first-hand observation. Moreover, the books which he consulted were, as a rule, centuries old.[38] He tells us practically nothing concerning his own period, in which so many important changes were taking place. For example, there are repeated and detailed references to the founding and early history of Rome, but no direct allusion to the political and social changes brought about by the disintegration of the Roman Empire; trifles attributed to a period thirteen centuries earlier seemed to interest him more than the mighty developments of his own epoch. Again, although he writes upon law, he does not appear to have heard of the Justinian code issued a century before;[39] and in his chronology he fails to mention the proposal for a new era in chronology made also a century before his time by Dionysius the Less.[40]

Throughout the Etymologies there is a leading principle which guides Isidore in his handling of the different subjects, namely, his attitude toward words. His idea was that the road to knowledge was by way of words, and further, that they were to be elucidated by reference to their origin rather than to the things they stood for. This, in itself, gave an antiquarian cast to his work. His confidence in words really amounted to a belief, strong though perhaps somewhat inarticulate, that words were transcendental entities. All he had to do, he believed, was to clear away the misconceptions about their meaning, and set it forth in its true original sense; then, of their own accord, they would attach themselves to the general scheme of truth. The task of first importance, therefore, in treating any subject, was to seize upon the leading terms and trace them back to the meanings which they had in the beginning, before they had been contaminated by the false usage of the poets and other heathen writers; thus the truth would be found. It was inevitable that, with such a preconception, Isidore’s method in the Etymologies should be to treat each subject by the method of defining the terms belonging to it.

It is plain, then, that Isidore used the dictionary method in the Etymologies not as a matter of convenience, but on philosophic grounds. His unthinking confidence in words was, however, ill-rewarded. It merely furnished a plan of treatment which evaded consecutive thought, and made it possible for his work to be a mass of contradictions, as it really is in very many points. Indeed, the task of combining in one work the ill-digested ideas of the school of Christian thought of his day and conflicting ideas borrowed from the pagans would not have been possible except to a writer who did not reason on his material, but was satisfied, as was Isidore, to give the derivation and meaning of his terms in the blind trust that a harmonious whole was thus constituted.

We have some information in regard to the production of the Etymologies.[41] It was a work undertaken at the request of Braulio, bishop of Saragossa, and it occupied the last years of Isidore’s life. Parts of it, however—presumably those that could be used as text-books—were in circulation before his death. Braulio is our authority for the statement that the work as a whole was left unfinished, and that he himself divided it into twenty books, Isidore having made no division except that by subjects. As the brief preface, addressed to Braulio, informs us, the work was the product of long-continued reading, and contained verbatim extracts from previous writers, as well as Isidore’s own comments.