ARS EST ARBOR, homo est arbor, scientia est arbor, anima est arbor (‘Art is a tree, man is a tree, knowledge is a tree, the soul is a tree’): these Latin statements were so common during the twelfth and thirteenth centuries, when tree frameworks represented simultaneously anthropological and cosmological conceptions, that their value as a cultural indicator is often overlooked by modern scholars. Originally attributed to Aristotle by Diogenes Laertius, the statement above reflects on the sweetness of the fruits of science with respect to the bitter efforts required to discover the principles of knowledge, whose roots lie deeply hidden in nature. From Late Antiquity to the Middle Ages this multidirectional approach to the discovery and creation of knowledge was transmitted via visual representation. This paper goes beyond revisiting the multiple instances of tree structures in the medieval scientific tradition. Indeed, my aim is to demonstrate how the conceptual structures of medieval scientific thought owe their development to arborescent structures. However, without conceptual references and an understanding of their pragmatic contexts these representations cannot be effectively understood; I therefore adopt a historical perspective which also allows for consideration of their philosophical aspects.

Ramon Llull (1232–1315) extended the Aristotelian statement cited above by drawing an analogy between the perceived motion of thought in progress and the natural growth of flowers as they appear on branches, following the movement of nutrients to the buds: