II. Astrological Philosophy
Plato, Ptolemy & Plotinus


Section Headings

Plato’s promotion of Astrology inspires the Greeks

Plato: Stars manifest Divine Order

Ptolemy: Astronomy Orderly, Astrology Useful

Ptolemy’s Physical Philosophy of Causation

Plotinus’ Philosophy of Mystical Correspondences

Plotinus: Free Will subject to Divine Justice


Plato’s promotion of Astrology inspires the Greeks

The ancient Chaldeans developed the main astrologic tradition. However, it remained for the Greeks with their advanced mythology and superior astronomical technology to carry it to the state described by Ptolemy. It was they who observed the heavens in fine enough detail that a precise planetary/stellar conception could be formulated.

Prior to the Greeks, there had only been the Sun, the Moon and the rest of the stars. It is under the Greek influence that the conception of cosmic spheres comes in, complete with the notion of the planetary spheres and the sphere of the Zodiac. This structuralized cosmic conception had vast implications for the art of astrology.

Prior to the Greek influence celestial divination was based upon the visible appearance of the sky. After the cultural synthesis, astrology came to be based upon the theoretical conception of the sky’s structure. Lindsay makes a strong case for the idea that it was Plato who provided the impetus that carried the Greeks to their advanced theories.

 “It was only much later, through the brilliant reputation of Plato, that the esoteric was removed from astronomical studies and access to them opened up for all … because he made natural laws subordinate to the authority of divine principles.” (Lindsay, p. 101)

The Greek establishment in the centuries before Plato had, in fact, worshipped the celestial bodies as gods. With the disillusionment with the old ways and customs that arouse during and after the long and exhausting Peloponnesian Wars between Athens and Sparta, the old values and gods came to be doubted (were called into question). In reaction to this new mood of skepticism, the Greek establishment began executing the intellectuals they felt to be the cause of this decay. (It was in this mood that Socrates was condemned and executed.)

It was through Plato’s writing and efforts on the behalf of the study of astronomia, which supplied the material representations of his perfect Forms, that the Greek populace began to accept the science of the stars.

Plato: Stars manifest Divine Order

Plato’s thesis, in contrast to the skepticism pervading the era, was that a divine order indeed existed. The gods were not dead as the Sophists argued, but instead manifested themselves in the divine order of the cosmos.

“Plato in the Timaios brought to a head the Pythagorean trend to look on Order, expressed in Number, as something controlling earthly existence, and thus above it, not merely incarnated in it. “ (Lindsay, p.96)

And from Plato’s Epinomis:

“Every diagram and system of number, and every combination of harmony, and the agreement of the revolutions of the stars must be manifest and will be made manifest if a man learns aright by keeping his gaze on unity. For it will be manifest to us that there is one bond naturally uniting all these things. But if one goes about in some other way, one must call on Fortune [Tyche] as we also put it.”

It seems that Plato calls upon us to put ourselves in touch with the divine order made manifest in the effect of the stars upon our world. Without this connection to the divine we can only rely on blind luck.

The only way, though, that we can put ourselves in touch with these divine rhythms is by actual inspection and understanding of the rhythms. It is not enough to merely observe the divine Form, one must also attempt to come to grips with the divine Form beneath the surface appearances. We must attempt to understand the cosmic laws.

“The choric dance of these same stars and their crossings one with another, and the relative reversals and progressions of their orbits … send [calamity] upon men unable to calculate alarming portents of the things which will come to pass later on; to describe all this without an inspection of models [mimemata] of these models would be labor in vain.” (Plato’s Timaios; Lindsay p 96)

Plato reconciles the old astral traditions with the new science in a subtle synthesis. There were two responses to Plato’s merger of astronomy and star-based divination. The first response was to transplant their old gods with their myths onto the planets and stars. Plato in Laws suggests that Apollo and Delos (the Sun) are the same composite god. This association of gods with planets must be potent, as it has persisted into modern times. Even today in the 21st century, everyone, even the non-believers, knows that the planet Venus is associated with women and beauty and that the planet Mars is associated with men and wars.

The second response was to focus on more systematic observations combined with theory. While the first was mythological (symbolic), this second trend has scientific underpinnings. Indeed, it ultimately led to the development of modern science. The desire to place a Number (mathematics) upon astronomical patterns, specifically planetary, led to a very advanced form of spherical geometry. For the very first time, mathematics enabled astronomers to make relatively accurate predictions about the future. The Greek success has inspired natural scientists all the way to Galileo and beyond to describe other natural patterns with mathematics.

“It was in the 3rd century that the Mesopotamian practice of divination by the stars was introduced to the Greeks. If the special mental climate of Greek civilization be borne in mind (i.e. the effect of the intimate blending of the Greek’s own personal gods with the borrowed astral gods, and the intellectual prestige given to this new religious conception by the brilliant new geometrical astronomy with which it was combined) it can be readily understood that the Greeks transformed astrology into something unknown in the land of its origin.” (Encyclopedia Britannica p 641)

As we’ve seen, Chaldean and Greek astronomia differed in two primary ways. Chaldean astrology was national; Greek astrology was individual. Chaldean astronomy was primarily observational; Greek astronomy concerned itself with models.

Ptolemy: Astronomy Orderly; Astrology Useful

The Greek system-building tendency finds its culmination in Ptolemy. As the leading astronomer, mathematician and astrologer of his time, what is Ptolemy’s opinion regarding the relative differences between the science of the heavens and the art of divination?

There was only one term for the study of the heavens in pre-Christian times, astronomia. Astronomia included both astronomy, the science of observation and measurement of the positions of the celestial bodies, and astrology, the study of the effects of these celestial bodies on the earth. Ptolemy begins with this distinction between astrology and astronomy.

Ptolemy claims that astronomy is “first in order and in effectiveness.” (Ptolemy, p3) Ptolemy was in fact the classical authority on astronomy. He refers the reader to his own book, the Almagest, on the subject. This book in parallel fashion to the Tetrabiblos “sums up the whole achievement of ancient astronomy.” (Encyclopedia. Britannica. p. 641A)

What an achievement! Ptolemy develops the ultimate astronomical model in one book. Then he writes another book that applies the new mathematical conception of the planets to human affairs through astrology.

In Ptolemy’s system, astronomy comes first. Astrology is “second and less self-sufficient”. Although astronomy is first, “it does not attain the result given by its combination with the second [astrology].” Astrology produces a unique result.

He warns however of the limitation of the astrological art.

“One whose aim is the truth might never compare its [astrology’s] perception with the sureness of the first, unvarying science [astronomy], for he ascribes to the weakness of and unpredictability of material qualities found in individual things.” (Ptolemy, p. 4)

While the stars and planets observe regular laws with respect to each other, the application of these precise laws to the earthly material plane of human existence can only be weak and irregular in direct relation to the nature of earthly existence, which is weak and unpredictable. Ptolemy sets up the distinction, traceable back to Plato’s dialogues, between the divinely regular stars and planets and the weak irregular mutable plane of human existence.

While “most events of a general nature draw their causes from the enveloping heavens”, there are any other causal facts found in events of an individual nature.

“But in an inquiry concerning nativities and individual temperaments in general, one can see that there are circumstances of no small importance and of no trifling character, which join to cause the special qualities of those who are born. Differences of seed, … places of birth, … rearing and customs, … . Unless each one of these things is examined together with the causes that are derived form the ambient (stars), although this latter be conceded to exercise the greatest influence.” (Ptolemy, pp. 18-19)

Although the stars exert an effect on individual affairs, they are only one of many casual factors.

Just as Ptolemy warns the adherents of astrology of the danger of astrological fallibility he also warns astrology’s opponents of rejecting astrology entirely just because it is not 100% accurate.

“Since this is the case, it would not be fitting to dismiss all prognostication of this character because it can sometimes be mistaken …, but as when the claims are great, so also when they are divine, we should welcome what is possible and think it enough. Nor, further, should we gropingly demand everything of the art, but rather join in the appreciation of its beauty, even in instances wherein it could not provide the full answer.” (Ptolemy, p 19)

It is obvious from this statement that Ptolemy suggests a very tolerant and multi-variable approach to astrology.

Ptolemy’s Physical Philosophy of Causation

Unlike Plato, Ptolemy seeks to explain the effects of the stars in purely physical terms. The sun has an obvious and marked effect upon earthly activities. The moon, also, has a lesser but still marked effect upon our planet. He reasons that it is probable then that the planets and collective stars exert some additional modifying influence.

“Their aspects to one another, by the meeting and mingling of their dispensations, bring about many complicated changes. For though the sun’s power prevails in the general ordering of quality, the other heavenly bodies aid or oppose it in particular details, the moon more obviously and continuously.” (Ptolemy, p. 18)

That the heavenly bodies have an effect upon the earth is understandable but why should the configurations of the heavens at the time of birth have any significance? Ptolemy argues that the nature of the seed reveals the nature of the grown plant; in a similar way the natal horoscope reveals the nature of the adult humane.

“The more observant farmers and herdsman, indeed conjecture from the winds prevailing at the time of impregnation and of the sowing of the seed, the quality of what will result; and in general we see that the more obvious configurations of sun, moon, and stars are usually known before hand.” Ptolemy , p.21)

He reasons that because the stars are regular and predictable that humans are also.

Plotinus’ Philosophy of Mystical Correspondences

At the same time that Ptolemy was describing the probability of stellar influence in physical terms, Plotinus (205-270 CE) describes the same astrological phenomena in mystical terms. In the Enneads, Plotinus first argues that the effect of the celestial bodies upon the Earth is not physical but is instead symbolic. The planets and stars do not cause terrestrial happenings; they are merely symbolic devices that indicate trends.

“Like birds of augury the living beings of the heavens, having no lot or part with us, may serve incidentally to foreshadow the future, but they have absolutely no main function in our regard.” (Plotinus, p.93)

He begins with the argument that even if the stars had a physical effect, their effect would be too general to affect what is attributed to them.

“Suppose them [the planets] to be without Soul. …any communication from them will affect only our bodily nature … This implies that no considerable change can be caused in the bodies affected, since emanations merely corporeal cannot differ greatly from star to star. Can it bring about such conditions as in no sense depend upon the interaction of corporeal elements? … good fortune at a particular moment?” (Plotinus, p. 92)

The physical effects of the stars would too general and diffuse to affect individuals.

Plotinus’ second primary argument is that if the effect of the stars is primarily physical that they could in no way interact in the fashion attributed to them.

“It is absurd to think that the grouping under which a star passes can modify either its character or earthward influences. … And why would there be any differences as a given star sees certain others from the corner of a triangle or in opposition or at the angle of a square? … And, the cardinal question: by what conceivable process would they affect what is attributed to them?” (Plotinus, pp. 92-94)

Because of these two reasons, Plotinus rejects the notion of a physical planetary influence.

Although Plotinus dismisses the physical role of the stars on the Earth, he acknowledges the usefulness of the stars as a divine sign or symbol for the universal harmonies.

“But all the stars are serviceable to the Universe, and therefore can stand to each other only as the service of the Universe demands, in a harmony like that observed in the members of any one animal form. They exist essentially for the purpose of the Universe - but all the members will be in sympathy with the entire animal frame to which they belong. Only so can there be a unity and a total harmony. And in such a total, analogy will make every part a Sign. “ (Plotinus, p 95)

In the tradition of the Pythagoreans, traceable through Plato, Plotinus posits a divine order where everything is in harmony and consequently related to all the other parts.

Actually one must imagine that this mystical explanation of planetary influence was more prevalent in the Hellenistic times than the theory of physical causation posited by Ptolemy. The Stoic school of philosophy which supported astrology had a much more complex notion of stellar influence than a simple cause and effect hypothesis.

“However many irrationalities were involved, we must at least realize that the astrologers were not making a mechanistic connection between a decan or a star and a limb of the body. Especially in the notion of a vital influence of sun and moon on our bodies, they were carrying on the Stoic doctrine of universal sympathy, of a continuum of tensional fields dynamically interacting and affecting all bodies on which they impacted - the bodies themselves being composed of energies, of pneuma, which made them akin to the rest of the universe, including the stars. The system also inherited the Pythagorean sense of endlessly entwining harmonies reducible to proportion. … To think merely of stars exerting some magical influence is to fail to get inside the astrologic systems. … These men were thinking of bodies, not as isolated mechanistic systems, but as bundles of energies, held together by what the Stoics called the hegemonikon and continually reshaped by a formative principle shared by the whole cosmos.” (Lindsay, p. 12)

Although Ptolemy attempts to establish a physical basis for his astrology - a natural tendency since he was first and foremost an astronomer; the actual philosophical base for astrology, as seen by the views of the popular Stoic school, is the idea of universal harmonies described by Plotinus.

Plotinus: Free Will subject to Divine Justice

The idea-complex of universal harmonies sidesteps the problem of free will and determinism that the celestial causalists find so disturbing. Even Ptolemy doesn’t attribute full causal powers to the stars, as pointed out before. Plotinus, referring back to Plato’s Timeaus, which, as we found, was so instrumental in justifying astrology to the Greeks, posits two forces, the Soul, which yearns towards the One, and temperament, which is under the control of the stars.

“Soul, then, in the same way is intent upon a task of its own; in everything it does it counts as an independent source of motion; it may take a direct course or it may divagate, but a Law of Justice goes with every action in the Universe, which otherwise, would be dissolved and is perdurable because the entire fabric is guided as much by the orderliness as by the power of the controlling forces. And in this order the stars, as being no minor members of the heavenly system, are cooperators contributing at once to its stately beauty and to its symbolic quality. Their symbolic power extends to the entire realm of sense, their efficacy only to what they patently do.” (Plotinus, p. 97)

Because man has Soul, he has free will, but any action taken is presided over by a divine Justice, which causes all action to inevitably fall in line. The stars seem to order or reflect the action.

“In the Timaeus, the creating God bestows the essential of the Soul, but it is the divinities moving in the Cosmos (the stars) that infuse the powerful affections holding from Necessity. - … By this statement our personality is bound up with the stars, whence our Soul takes shape; and we are set under Necessity at our very entrance into the world; our temperament will be of the star’s ordering, and so, therefore the actions which derive from temperament.” (Plotinus, p. 97)

Although humans have freedom of choice because of the divine Soul, all movement must fall inevitably in line with the universal harmony, which is revealed by the symbolic nature of the stars.


Reviewing, the Chaldean/Babylonians provided the foundations of astrology. The Greeks took it to a new level, basing their astrology upon a mathematical understanding of planetary position. Ptolemy’s Tetrabiblos was the culmination of this trend. Due in part to this new conception of the heavens, the Greeks became interested in the underlying philosophy of astrology – a viewpoint that was lacking in prior cultures.

“With regard to the aim, we may note that the Babylonians were primarily concerned with reading omens and improving the calendar, while the Greeks were attempting to relate astronomy to a general conception of the cosmos as a whole.” (Lindsay, p88)

Plato justified the notion of stellar correspondences to the Hellenistic intellectual in terms of a symbolic effect. Ptolemy argued that the effect of the stars, while very subtle, was indeed physical. Plotinus, around the same time, points out many fallacies in an astrological theory that claims a physical effect of the stars. He points to a divine order, which makes everything a symbol, the stars and planets as the primary symbol.

The other articles in the series:

I. A Brief History of Astrology: Chaldeans -> Greeks -> Ptolemy

III. Ancient vs. Modern Astrological Practices


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