Porphyrian Trees
A Logic Exercise
Porphyry was a neoplatonic philosopher who lived c. 234-305 A.D. He was born in Tyre of Phoenicia during the time when the Roman Empire was beginning to wane in its power. He is best known for editing and publishing The Enneads ( the collection of writings by the philosopher Plotinus who was his own teacher), for his own book Isagoge which is a kind introduction to logic and philosophy, and for his book Against the Christians. Despite his deep antagonism toward Christians (whom he blamed for weakening the Roman Empire through their religion) his work in the realm of Logic was deeply influential among Christian thinkers throughout the middle ages.
One of the contributions left to the world by Porphyry is what has come to be known as “Porphyrian Trees.” These diagrams are meant to help a thinker analyze the base nature of any given thing by running through a series of basic binary (yes or no) questions. Here are the basic questions we may ask about any given thing:
Does it have being (existence)?
Is it material?
Is it living?
Is it sentient?
Is it rational?
These questions can be placed upon a chart (see figure 1 below) to help us see the flow and to map out the base nature of any particular thing. Each time a person can answer in the affirmative to these questions as he moves down the list this is called a note in logic. If, for instance, a “table” is under consideration we may ask whether or not it has being (i.e. do tables exist)? Yes (1 Note). Are tables material beings? Yes (2 Notes). Are tables living? No. There is no need to continue with the other two questions at this point because no non-living thing can be sentient or rational. So, of a table’s base nature we may say it has two notes because it is a non-living, material being. A simple definition of a table, then, is “a non-living material being.” The phrase “non-living” is not considered a note but is included in our final answer because it tells us where we came to a “dead-end” on the Porphyrian Tree.
If, however, we consider what a man is we will find that we can go all the way through the tree. Does man have being? Yes (1 Note). Is man material? Yes (2 Notes). Is man living? Yes (3 Notes). Is man sentient? Yes (4 Notes). Is man rational? Yes (5 Notes). So, we may define man as “a kind of rational, sentient, living, and material being.” It is perfectly right to acknowledge that man is more than this, but the purpose here is to define something’s base nature. In other words, we cannot rightly say man is anything less than this. Other approaches to defining or determining the nature of a thing may also be helpful to gain even more precision in our definitions, but Porphyry's Trees are a decent place to start if we want to get down to the bottom of a thing and work our way up from there.
Helpful Definitions:
Being: the state of existing.
Organism: a living, material being.
Sentient: in possession of senses such as touch, taste, hearing, smelling, or sight.
Rational: capable of making judgments about truth claims.
Porphyrian Tree: Exercise
Making use of this lesson (and the above figure of a complete Porphyrian tree) give a base definition of the following things and tell how many notes it has.
Dog
Definition:
Number of Notes: _________
Tree
Definition:
Number of Notes: _________
Book
Definition:
Number of Notes: _________
Angel
Definition:
Number of Notes: _________
Sphinx
Definition:
Number of Notes: _________
Memoria Press has a great logic book/course that utilizes these trees. It's fun to teach!
Very interesting. I hadn’t come across this before, but it is helpful.