According to Plato, a core of mathematical knowledge – later known as the Quadrivium – was essential for an understanding of the Universe. The curriculum was outlined in Plato’s *Republic*. The name Quadrivium means four ways, but this term was not used until the time of Boethius in the 6^{th} century AD [see TM119 or search for “thatsmaths” at irishtimes.com].

It is said that an inscription over the entrance to Plato’s Academy read “Let None But Geometers Enter Here”. This indicated that the Quadrivium was a prerequisite for the study of philosophy in ancient Greece.

**The Four Arts**

The Quadrivium originated with Pythagoras around 500 BC. The Pythagoreans sought the unchanging fundamentals underlying nature and society. Their quest was to find the eternal laws of the Universe, and they organized their studies into the scheme later called the Quadrivium. It arises from number, the subject revered by the Pythagoreans, and comprises four disciplines.

The first is Arithmetic, concerned with the infinite linear array of numbers. Moving beyond the line to higher-dimensional spaces, we have Geometry. The third discipline is Music or Harmony which is, fundamentally, an application of the pure science of numbers evolving in time. Fourth comes Astronomy, the application of Geometry to the world of space.

Pythagoras distinguished between quantity and magnitude. Objects that can be counted yield quantities or numbers. Substances that are measured provide magnitudes. Thus, cattle are counted whereas milk is measured. Arithmetic studies quantities or numbers and music involves the relationship between numbers and their evolution in time. Geometry deals with magnitudes and astronomy with their distribution in space.

A key person in this organization was Archytas, who flourished in Tarentum (Southern Italy) around 400 BC. He was one of the last scholars of the Pythagorean School and was the founder of mathematical mechanics, as well as a good friend of Plato. The designation of the four disciplines of the Quadrivium is ascribed to Archytas. His views were to dominate pedagogical thought for over two millennia and it is in some measure due to Archytas that mathematics has played such a prominent role in education ever since.

**Boethius**

The Western Roman Empire was in many ways static for centuries. Nothing new was contributed to mathematics between the conquest of Greece and the fall of the Roman Empire in AD 476. Boethius, the 6^{th} century Roman philosopher, translated Greek texts on the subjects of the Quadrivium, including Euclid on geometry and Ptolemy on astronomy, and also wrote texts on arithmetic and music. Although his books were poor copies of earlier work and contained nothing original they were considered authoritative, and were studied by medieval Irish monks.

The organization of the Quadrivium was formalized by Boethius, and this structure endured for over a millennium. It was the mainstay of the medieval monastic system of education, which had a structure of seven subjects – the seven liberal arts – comprising the Trivium and the Quadrivium. The Trivium was centred on three arts of language: grammar, ensuring proper structure of language, logic for arriving at the truth and rhetoric for the beautiful use of language. Thus, the aim of the Trivium was goodness, truth and beauty. In the modern era, mathematics writer Morris Klein classified the four subjects of the Quadrivium as pure (arithmetic), applied (music), stationary (geometry) and moving (astronomy).