by Bruce Scofield

From the height of the Roman Empire to the Renaissance, the scientific writings of a single author defined both astronomy and astrology. Claudius Ptolemy (c. 150), often referred to as the greatest scientist of the ancient world, was the author of the Almagest (or Syntaxis Mathematica), a detailed, mathematically sophisticated work on the movements of the solar system. In it the circular motions of the Sun, Moon and planets in an Earth-centered universe were explained and demonstrated. In order to do this, Ptolemy’s mathematics moved towards trigonometry, and in regard to his analysis of angles using chords, he is credited with being one of the founders of that branch of mathematics. The geocentric cosmos that Ptolemy mathematically modeled could predict with reasonable accuracy where amongst the stars the Sun, Moon and planets could be found in the future. The need to refine this useful model was therefore not pressing and so the Earth remained at the center of the cosmos in the minds of natural philosophers for centuries. Even Copernicus, whose heliocentric model produced only slightly better results, hesitated to topple this ancient structure.

In addition to astronomy, Ptolemy authored a major work on astrology. The work is generally known as the Tetrabiblos or Quadripartitum (four books on astrology) though the title Mathematical Treatise in Four Books is found in some manuscripts.1 In it, Ptolemy introduced the subject material of astrology, organized it into sections, and discussed it theoretically. He treated astrology as a demonstrable system, with consistent rules and methods, but he gave no examples or indication that he actually practiced it. His masterful description defined the boundaries of the astrology and raised it to the status of a science, and placed its contents in an order that has been followed, for the most part, ever since.

Ptolemy approached astrology as a systematic description of nature that requires prerequisite knowledge of astronomy, mathematics, and natural philosophy. Astronomy, which he expounded in great length in the Almagest, he defined as:

That whereby we apprehend the aspects of the movements of the Sun, Moon and stars in relation to each other and to the Earth as they occur from time to time. 2

Astrology he defined as:

That in which by means of the natural character of these aspects themselves we investigate the changes which they bring about in that which they surround.3

According to Ptolemy, astrology is a less exact, and less self-sufficient, science than astronomy, which deals, for the most part, with perfect spheres. Astrology is characterized by the unpredictability of the material qualities found in individual things and presents problems because certain parts of it are so difficult for some to understand that they come to regard the subject itself as incomprehensible. Having stated these problems, Ptolemy began his exposition of the subject matter with a stated intention to examine both the possibility and usefulness of astrology.

At the start of the second book Ptolemy made an important distinction in regard to the subject of astrology, and one that is central to my thesis – the division of astrology into two fundamental categories: universal, or general, and genethlialogical. The former is concerned with natural phenomena such as regional and collective factors, climate, weather, agriculture, plagues, etc., and the later was concerned with the affairs of individual humans. Universal astrology encompassed genethlialogical astrology; that is human-centered astrology ultimately yielded to the larger and more general influences of universal astrological influences. This is how Ptolemy defined universal or general astrology:

Of the general inquiry itself, a part, again is found to concern whole countries, and a part to concern cities; and further, a part deals with the greater and more periodic conditions, such as wars, famines, pestilences, Earthquakes, deluges, and the like; and another with the lesser and more occasional, as for example the changes in temperature in the seasons of the year, and the variations of the intensity of storms, heat, and winds, or of good and bad crops, and so on.4

This distinction was accepted for the most part for the next 1500 years although, due to the complications raised by the nature of medical astrology, the subject matter of political prognostications, and the varying approaches to the subject by individual practitioners, it can be argued that astrology might be divided in other ways. However, by the late Middle Ages, these two general branches were still distinguished by writers on the subject and had come to be identified as natural and judicial astrology. Judicial astrology subsumes three practices: nativities, which concern the temperament and life history of humans, questions or interrogations which are the immediate concerns of humans, and elections, the times during which humans consciously choose to take action. The only area of inquiry within the domain of natural astrology that concerns humans has to do with the experiences faced by groups, cities and regions. This component of natural astrology regards the experiences of human collectives as similar categorically to the experiences of the Earth itself when changes in weather, earthquakes, etc. occur. Both human collectives and the Earth are subject to the same influences from the Sun, Moon and planets and the same astrological methodologies have been applied to both. Today this component of natural astrology is sometimes referred to as mundane astrology.5

In addition to these distinctions, Ptolemy also offered a mechanism for astrology. In the first book of the Tetrabiblos, Ptolemy very briefly addressed the problem of exactly how the Sun, Moon and planets, and also stars, actually produce effects on the Earth, its processes and inhabitants. Ptolemy explained astrological phenomena in a way that differs somewhat from that of Aristotle.6 The later’s doctrine involved the transmission of motion from the outer celestial sphere downwards towards the Earth. Ptolemy argued that the planets have their own life force, can move themselves and they move with respect to each other like a flock of birds, each pacing themselves without touching. The planets also move in perfectly circular orbits by their own volition within a space-filling ether that is a medium through which motion-energy is transmitted. The motions of the Sun, Moon and planets then transfer their energy through the ether down to the sublunar region that is surrounded by the primary elements fire and air, which, in turn, transfer this energy to the more Earthly elements water and earth.7 Ptolemy’s definitions and distinctions between astronomy and astrology, and the subdivisions of the later, were maintained for centuries and are still relevant today.