Spotlight: a medieval tree of knowledge

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By | Early Medicine, From the Collections

Like modern-day students, medieval people used diagrams and images to reinforce learning and memorisation. In long and complex philosophical manuscripts, occasionally an image was used to break the monotony of reading. The tree diagram considered here was part of a tradition of visualising information and concepts relating to philosophy, medicine and other areas of learning.



Peter of Spain’s 13th century ‘Dialectica’ was one of the essential textbooks of medieval universities. It was part of his larger compendium the ‘Summulae logicales’, a work that would continue to be used by students up until the 17th century. The main aim of the ‘Dialectica’ was to provide a basis of philosophical investigation in a manner that was accessible to students, as Peter believed that this was the foundation for all other university education.

Wellcome MS. 55 is a miscellany produced between 1472 and 1474 in Leipzig by the historian Johann Lindner (1440–1524). Peter of Spain’s ‘Dialectica’ is the last of 11 works, following Aristotelian treatises and works attributed to other authors, including Gilbert of Poitiers and Albert the Great. The manuscript was acquired by Henry Wellcome in 1908.

The standout features of this manuscript are the detailed diagrams towards the end of the ‘Dialectica’, as well as the diagram of the human brain on folio 93 recto. The diagrams within the ‘Dialectica’ are rather elegant and tidy for what is a heavily glossed and, above all, well used manuscript. It seems that these pictographic learning aids were used with some care by early readers, as they lack the scrawling notes that envelop the rest of the volume.

One diagram, on folio 202 verso, uses the form of a tree to depict and arrange philosophical concepts. Such tree diagrams are commonly called ‘arbor porphiri’ or the ‘tree of Porphyry’. Despite its name, the illustration has very little to do with the Neoplatonist philosopher Porphyry (234?–305? AD), whose ‘Isagoge in logicam’ is one of the other texts in MS. 55. In fact, Porphyry only posited the suggestion of depicting philosophical concepts as a tree. Medieval scholars ran with this idea and brought it into being in numerous manuscripts.

In MS. 55 the tree is used to illustrate the relationship between ‘genera’ (‘types’) and ‘differentiae’ (‘differences’). Our illustrator looks to represent the connection between a subject (e.g. animal, man, plants, minerals) and its defining characteristics (e.g. whether it has a rational mind, whether it is able to move).

Five central ovals form the trunk of the tree. These are the ‘genera’: substance (at the top), body, living body, animal, man. The branches of the tree, the ‘differentiae’, sprout from each side of the trunk forming binaries with each other: corporeal and incorporeal, animate and inanimate, sensible (the ability to sense) and insensible, rational and irrational, and finally Socrates and Plato.

It may strike one as odd that Socrates and Plato are included as branches at the bottom of the tree. Socrates and Plato serve as examples of individual men, enabling the reader to work his or her way up the tree to categorise an individual person according to that person’s characteristics.

From looking at the neatly arranged ovals, we might question whether the illustration is a tree in any conventional sense. Indeed, the only way we can tell it is a tree is from the roots at the bottom. The roots ground the tree in the ‘arbor porphiri’ tradition, and make the diagram instantly recognisable to its medieval reader.

The tree diagram illustrates some of the concepts that were central to the medieval study of philosophy. Such ideas about the body, the mind and what it meant to be human were fundamental to the intellectual framework within which medieval medicine flourished.

Author: Patrick Outhwaite is a placement student at the Wellcome Library. He holds an MSt in Medieval Studies from the University of Oxford, and is currently undertaking an MA in Medieval English at King’s College London. His research interests include the interplay between medieval theology and medicine, as well as palaeography.

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