4/Historical Note

Historical Note on 4|$4$
The number 4|$4$, as was 8|$8$, was associated by the Pythagoreans with the concept of justice, being evenly balanced: $4 = 2 + 2$, where $2$ is the principle of diversity.

Throughout history, the number 4|$4$ has been regarded with particular significance.

There are $4$ humours:
 * Sanguine, Melacholic, Choleric, Phlegmatic.

There are $4$ cardinal points of the compass:
 * North, East, South and West.

In the Old Testament, there were $4$ rivers which watered the Garden of Eden:
 * Pishon, Gihon, the Tigris, and the Euphrates.

In Islam, these rivers are:
 * Saihan (Syr Darya), Jaihan (Amu Darya), Furat (Euphrates) and Nil (Nile).

In the New Testament, there are $4$ Gospels:
 * Matthew, Mark, Luke and John.

The most aesthetically pleasing musical intervals are those whose frequencies are associated with the ratio of $1 : 4$.