One of the results of Porphyry's conservative position toward traditional religious practice and belief was the 'return' to the doctrine that the stars and planets are capable of affecting and ordering human life. Plotinus argued that since the individual soul is one with the All-Soul, it is in essence a co-creator of the Cosmos, and therefore not really subject to the laws governing the Cosmos -- for the soul is the source and agent of those laws! Therefore, a belief in astrology was, for Plotinus, absurd, since if the soul turned to beings dependent upon its own law -- ., the stars and planets -- in order to know itself, then it would only end up knowing aspects of its own act, and would never return to itself in full self-consciousness. Furthermore, as we have seen, Plotinian salvation was instantly available to the soul, if only it would turn its mind to "essential being" ( see above ); because of this, Plotinus saw no reason to bring the stars and planets into the picture. For Porphyry, however, who believed that the soul must gradually work toward salvation, a knowledge of the operations of the heavenly bodies and their relation to humankind would have been an important tool in gaining ever higher levels of virtue. In fact, Porphyry seems to have held the view that the soul receives certain "powers" from each of the planets -- right judgment from Saturn, proper exercise of the will from Jupiter, impulse from Mars, opinion and imagination from the Sun, and (what else?) sensuous desire from Venus; from the Moon the soul receives the power of physical production (cf. Hegel, p. 430) -- and that these powers enable to the soul to know things both earthly and heavenly. This theoretical knowledge of the powers of the planets, then, would have made the more practical knowledge of astrology quite useful and meaningful for an individual soul seeking to know itself as such. The usefulness of astrology for Porphyry, in this regard, probably resided in its ability to permit an individual, through an analysis of his birth chart, to know which planet -- and therefore which "power" -- exercised the dominant influence on his life. In keeping with the ancient Greek doctrine of the "golden mean," the task of the individual would then be to work to bring to the fore those other "powers" -- each present to a lesser degree in the soul, but still active -- and thereby achieve a balance or sôphrosunê that would render the soul more capable of sharing in the divine Mind. The art of astrology, it must be remembered, was in wide practice in the Hellenistic world, and Plotinus' rejection of it was an exception that was by no means the rule. Plotinus' views on astrology apparently found few adherents, even among Platonists, for we see not only Porphyry, but also (to an extent) Iamblichus and even Proclus declaring its value -- the latter being responsible for a paraphrase of Claudius Ptolemy's astrological compendium known as the Tetrabiblos or sometimes simply as The Astronomy . In addition to penning a commentary on Ptolemy's tome, Porphyry also wrote his own Introduction to Astronomy (by which is apparently meant "Astrology," the modern distinction not holding in Hellenistic times). Unfortunately, this work no longer survives intact.