Nettleship, Lectures and Essays, Oxford, 1885, devotes attention chiefly to the encyclopedic tradition, treating of Verrius Flaccus, the Glosses of Placidus, the Noctes Atticae of Gellius, Nonius Marcellus, and Servius. He treats of Isidore only by the way, and lays stress on his debt to Suetonius, Prata, and Verrius Flaccus, De Verborum Significatu. See pp. 330–336, and for opinion of Latin encyclopedic tradition, pp. 283–285.
Reifferscheid, Suetoni Reliquiae, recovers several passages of Suetonius from Isidore.
C. Schmidt, Quaestiones de musicis scriptoribus Romanis imprimis de Cassiodoro et Isidoro, traces Isidore’s De Musica to an unknown Christian writer.
G. Becker, editor of De Natura Rerum, Berlin, 1857, discusses the sources of that work especially, tracing it to Suetonius, Solinus, and Hyginus on the one hand, and Ambrose, Clement, Augustine, on the other.
H. Hertzberg, Die Chroniken des Isidors, Forsch. zur deutschen Geschichte, 15, 280 et seq., discusses the sources of Isidore’s Chronica, which he traces to Jerome’s translation of Eusebius with later continuations. The same writer also treats of the sources of The History of the Goths (Gött. 1874).
H. Usener, Anecdoton Holderi (Bonn, 1877), p. 65, asserts that Isidore did not use Cassiodorus’ encyclopedia of the liberal arts.
M. Conrat, Geschichte der Quellen und Literatur des Römischen Rechts im früheren Mittelalter (Leipzig, 1891) treats of the sources of Isidore’s Leges, pp. 151 et seq.; as also Voigt, Jus Naturale, 1, 576 et seq., and Dirksen, Hinterlassene Schriften, 1, 185 et seq.
Arno Schenk, De Isidori Hispalensis de natura rerum libelli fontibus, Jena, 1909, finds that Isidore wrote the De Natura Rerum and the Etymologiae from his collection of excerpts which is drawn from Ambrose, Clement, Augustine, Jerome, the scholiast on Germanicus, Hyginus, Servius, the scholia on Lucan, Solinus, Suetonius, and a number of the Roman poets. This dissertation is largely meant to show that Reifferscheid in his work, Suetoni Reliquiae, had gone too far in attributing passages found in Isidore to Suetonius.
M. Klussman, Excerpta Tertullianea in Isidori Hispalensis Etymologiis, Hamburg, 1892, gives a list of nearly seventy passages borrowed by Isidore from Tertullian, at the same time pointing out that credit for the passages is nowhere assigned to the latter.
[55] For example, Isidore evidently had a theory as to the origin and value of language, but he does not state it anywhere, although innumerable times he approaches the subject in an oblique sort of way. See [p. 99]. Again, he never tells us whether he believed the earth to be flat or spherical; he uses at one time language that belongs to the spherical earth, and at another, language that can have sense only if he believed the earth to be flat. Here we have not only no definite statement of the conception—although it must have existed in his mind, considering the frequency of his writings on the physical universe—but we have in addition the puzzle of deciding which set of expressions used in this connection was meaningless to him. See pp. [50]–[54] and [Appendix].