The Tree of Porphyry

The Tree of Porphyry is a logical diagram that serves as a visual tool for explaining the hierarchy of genera and species in Aristotle’s classification system. This scheme gained widespread recognition in the Middle Ages thanks to the works of Neoplatonists such as Boethius and Peter of Spain.

In manuscripts, various versions of the Porphyrian Tree diagram can be found. Some of them include only nodes, representing the main concepts and categories. In these schemes, the focus is exclusively on the key blocks without indicating the relationships between them.

Aarau, Aargauer Kantonsbibliothek, MsMurF 84: Petrus Hispanus, Petrus Tartaretus. p. 94v. 15th century. (https://www.e-codices.unifr.ch/en/list/one/kba/MurF0084)

Other versions of the diagram include edges showing the connections between the dichotomous nodes. These edges illustrate the relationships between genera and species, making the structure clearer and more comprehensible.

Einsiedeln, Stiftsbibliothek, Codex 315(605): Boethius, Isagoge. p. 53. 10th century. (https://www.e-codices.unifr.ch/en/list/one/sbe/0315)

According to one version, the term “Tree” (Arbor) to describe the scheme was first used by Peter of Spain in his treatise “Summulae Logicales.”

All this is clear in the figure called the tree of Porphyry.

Inspired by this idea, manuscript illustrators began to depict the Porphyrian Tree as an actual tree, adorning it with plant motifs and transforming the abstract diagram into a work of art.

The structure of the Porphyrian Tree reflects the hierarchy of being, starting from the highest genus — substance — and ending with the lowest species, which cannot be further divided. It includes individual entities such as Socrates and Plato.

Between the highest genera and the lowest species, there are intermediate levels that function simultaneously as genera and species. As one moves from genus to species, the description of the subject is supplemented with increasingly specific distinguishing features.

To determine the position of humans in this hierarchy, one must traverse the tree, starting from the most general concepts and moving towards the more specific ones.

The Porphyrian Tree in сomputer science

The Porphyrian Tree can be classified as a general tree because, in this data structure, each node can have any number of child nodes.

St. Gallen, Stiftsbibliothek, Cod. Sang. 817: Aristotle · Boethius · Remmius Favinus (?). p. 341. 11th century. (https://www.e-codices.unifr.ch/en/list/one/csg/0817)

const arbor = [
  {
    'name': 'Substance',
    'children': [
      {
        'name': 'Corporeal',
        'children': [
          {
            'name': 'Animate',
            'children': [
              {
                'name': 'Sensible',
                'children': [
                  {
                    'name': 'Rational',
                    'children': [
                      {
                        'name': 'Mortal',
                        'children': [
                          {
                            'name': 'Socrates',
                            'children': [],
                          },
                          {
                            'name': 'Plato',
                            'children': [],
                          },
                        ],
                      },
                      {
                        'name': 'Immortal',
                        'children': [],
                      },
                    ],
                  },
                  {
                    'name': 'Irrational',
                    'children': [],
                  },
                ],
              },
              {
                'name': 'Insensible',
                'children': [],
              },
            ],
          },
          {
            'name': 'Inanimate',
            'children': [],
          },
        ],
      },
      {
        'name': 'Incorporeal',
        'children': [],
      },
    ],
  },
];

📖 Language in dispute: an English translation of Peter of Spain’s Tractatus, called afterwards Summulae logicales: on the basis of the critical edition established by L.M. de Rijk

📖 Neoplatonic “Tree of Life”
(Arbor Porphyriana: A diagram of logic and mystical theology)
Amer Dardağan

📖 The Medieval Tree of Porphyry: An Organic Structure of Logic
Annemieke R. Verboon