The term "element" (Ar. ʿunṣur , pl. ʿanāṣir ) is commonly used to refer to the four elements found in nature, according to classical Greek and mediaeval (including Islamic) science-namely, fire, air, water, and earth. An equivalent Arabic term, borrowed from the Greek στοιχεῖον (stoicheion) via Syriac, is usṭuqus (pl. usṭuqusāt ). Aristotle credits Empedocles (c. 495-35 B.C.E.) with being the first to formulate the theory of the four elements that underlie all material substances. These elements could be found combined in natural substances (for instance in blood, which