ADELARD of Bath. — An Englishman by birth, he completed his studies in Tours and taught in Laon. Dissatisfied with the “gallica studia,” he undertook long journeys to southern Italy, Sicily—where he enjoyed the favor of Bishop William of Syracuse— the Near East, and Palestine. His direct familiarity with the scientific works of the Greeks and Arabs provided him with new and important materials for his favored studies in physics, astronomy, and mathematics. Upon his return to his homeland, he apparently obtained some teaching position at the royal court; in the meantime, he devoted himself to compiling treatises in dialogue form and preparing translations to make the philosophy and sciences of Mediterranean culture accessible to the West. His death is placed around 1160.
His works certainly authentic are: *De eodem et diverso*, ed. H. Willner (*Beiträge zur Geschichte der Philosophie des Mittelalters*, IV, 1, Münster in V. 1909); *Per difíciles quaestiones naturales*, translated at the end of the 13th century into Hebrew, as M. Steinschneider demonstrated (*Die hebräische Übersetzung*, Berlin 1893, § 275, p. 464), and edited at the end of the 1500s; *Regulae abaci*, edited by Boncompagni in his *Bullettino di bibliografia e di storia delle scienze matematiche e fisiche*, 14 (1881), pp. 1–134; *Ezik Elkauresmi*, a version of the astronomical tables of al-Khuwarizmi (1126); *Elements of Euclid*, translated from Arabic; *The Astrolabe* and *De cura accipitrum*, which is a treatise on falconry (ed. A. E. H. Swain, Göttingen 1937).
In the controversy over universals, A. opposed exaggerated realism, and his solution makes him a precursor of Abelard. In the *Quaestiones naturales*, his spirit of observation frequently stands out, while he denounces the laziness of mere repeaters and calls authority the halter (*capistrum*) of the intellect. In physiology, he abandoned Aristotle in favor of Galen and the Salernitan physicians; he enunciated the principle of the continuity of nature and the indestructibility of matter and seems to have been the first among the Latins to use the way of motion to prove the existence of God. He occupies a position of the first rank in the development of science, not only of the 12th century but of the entire Middle Ages; he is the pioneer of the scientific method, which he knew how to unite with a refined taste for classical antiquity, revealed in his passionate researches for Greek and Arab works and recognizable in the unmistakable style of his writings, which recalls classical models.