Jolivet has shown in a very convincing manner (“Aux origines”) that the Arabic term šay’ and šay’iyya (thingness, or rather reality) had their own history,
quite independent of the Aristotelian *pragma* and connected with the debates in Islamic theology regarding the nonexistent, of which we still find an echo, after Avicenna, in Šahrastānī (“L’inexistant est-il une chose ou non?”), but whose more distant background goes back to al-Kindi and al-Fārābī and to the positions of the Muslim practice of theological debate known as kalam, for which the thing is what is known and every nonexistent is a “thing.”It is from this “formal ontology” centered on the “thing,” as it is elaborated on the basis of al-Fārābī and Ibn Sīnā, that algebra developed, outside Aristotelian epistemological frameworks, as a science common to arithmetic and geometry, bringing in the “thing,” res (al-šay’), as something unknown that can designate either a number or a geometrical magnitude (Rashed, “Mathématiques et Philosophie”).
Thus are sketched the outlines of a new ontology in which one can speak of an object without definite characteristics, and even know it, but not represent it exactly.
In the Latin translations of Arabic works on algebra that began to appear at the beginning of the thirteenth century, the term that was finally adopted to designate the unknown was thus res (res ignota), whereas in books on mathematics written in Italian, the word cosa appeared in the following centuries (cf. G. Crapulli, “Res e cosa (cossa),” and C. Costable and P. Redondi, “Sémantèse de res / cosa / cossa,” in Fattori and Bianchi, Res).
– Dictionary of Untranslatables, A Philosophical Lexicon
Edited by Barbara Cassin
Translation edited by Emily Apter, Jacques Lezra & Michael Wood