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] [35] “La Suma Teológica del Siglo VII.” Menéndez y Pelayo, _Estudios de Crítica Literaria_, vol. 1, p. 149. [36] If Isidore had been as thorough-going as Gregory in depreciating the secular he certainly would not have written the _Etymologies_. His strongest anti-secular spirit is shown in the chapter (13) _de libris gentilium_ of the _Sententiae_ where, following Gregory, he denounces “all secular learning.” It is pretty plain, however, that he is here following his model rather than working out his own position, and in the last section of the chapter he modifies what he has said by admitting that grammar may “avail for life if only it is applied to better uses.” 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. 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. [37] It is not of great length—three hundred and twenty-eight quarto pages in the reprint of Arevalo’s edition in Migne, _Patrologiae Latinae_, with about one-fifth of each page occupied by footnotes.