The Quadrivium

While speaking of groups of four, we owe another one to the Pythagoreans, the
division of mathematics into four groups, giving the famous Quadrivium of knowledge, the four subjects needed for a bachelor's degree in the Middle Ages.

                                                              Mathematics

                                        _____________|____________

                                        |                                                        |

                                Discreet                                          Continuous

         _____________|___________________________|________

       |                                  |                                        |                                |        

Absolute                     Relative                              Static                     Moving

      |                                    |                                       |                              |

Arithmetic                      Music                           Geometry              Astronomy