The standard Peripatetic view considers the primary qualities as constitutive, with the matter, of the substance of the body. Accordingly the only qualities responsible for any change are the four primary ones: hot, cold, moist and dry. However, properties of bodies like magnetic attraction are non-sensible powers that cannot be explained solely from the mixture of primary qualities. Such specific properties (khāwaṣṣ) would be the observable but unexplained physical manifestation of a specific power proper to some mineral, animal or plant. They can be observed but not deduced rationally. Of course alchemy made considerable usage of such properties or powers, but medicine also used the same notion extensively, especially in pharmacotherapy. Galen already acknowledges the phenomenon, distinguishing between drugs that act through their elementary qualities and those that act “through the peculiar property of their entire substance” without further explanation. The problem, which is at the intersection between medicine and natural philosophy, was precisely how to provide a causal explanation for the properties of a drug that apparently do not result from a mixture of the primary qualities. It will however receive much greater prominence in Avicenna’s medico-pharmacology that shifted the emphasis towards an empirical, non predictable model, relying solely on experience (McVaugh). This paper will examine some responses to Avicenna in the Arabic medical literature at the turn of the thirteenth century aiming at restoring a more speculative approach based on a causal and scientific explanation in terms of the primary qualities within Aristotelian physics.
