To mention only the best known of the twins recorded in the ancient tradition of our fathers, two twins were born at so short an interval of time that the second had a hold on the foot of the first. Yet, they were so unlike in their lives, character, conduct, and the love their parents bore them that this unlikeness made them enemies one of the other. When I say unlike, I do not mean that one would sit while the other walked, or that one slept while the other was awake, or that one talked while the other kept quiet—for these are the kind of differences that depend on the tiny variations of horoscopes which have to be neglected by those who observe the stars at the moment of birth with a view of consulting the astrologers.
One of our twins led a life of servile toil, while the other served no one. One was loved by his mother, the other was not. One lost the title to primogeniture, which was then so highly esteemed, and the other obtained it. Further, there were immense differences between them in regard to their wives, children, and possessions. If such differences are to be explained by those split seconds between the births of twins which are considered negligible in their horoscopes, why are such matters mentioned when other people’s horoscopes are in question? If, on the other hand, predictions are made about matters like these on the assumption that they do not depend on the negligible elements of time but on those moments which can be observed and set down, then what lesson can we draw from the potter’s wheel but this, that men have minds as malleable as clay that can be spun around and around without being able to stop to confute the absurdities of the astrologers.
A good way to refute those who attribute to the stars what depends on a similarity of bodily dispositions is to recall the two boys whom Hippocrates thought to be twins after he had examined medically the simultaneous fluctuations in their health. Considering that they could not be born at the same time, why did not one get sick after the other, in the order of their births, rather than that both should get sick in the same way and at the same time? Why did their sickness and recovery occur simultaneously and not successively, in the order in which they were born—for, certainly, they could not have been born simultaneously?
Or are we to suppose that being born at different times makes no difference in regard to falling sick? If so, why do the astrologers pretend that being born at different times makes a difference in regard to other matters? If they could travel at different times, marry at different times, beget children at different times, and so on, all because they were born at different times, why, for the same reason, could they not get sick at different times? Why should we go to the simultaneous conceptions to find a horoscope in regard to health, when succession in the moments of birth changes the horoscopes in regard to other matters?
On the other hand, if we are to admit that fate in regard to health depends on conception, while fate in regard to other matters depends on the hour of birth, then there ought to be no predictions about health from the inspection of natal stars—since from such an inspection nothing is known about the moment of conception. Or, if predictions are to be made in regard to health, even when no horoscope was taken at conception, on the ground that the moments of birth are sufficient, how could the sickness of either of our twins have been foretold from the moment of birth, since the fellow twin was fated to have the same hour of sickness, though he had a different moment of birth?
Another difficulty. Granted that there is enough difference in the time of the births of twins to call for different constellations on account of their different horoscopes and, consequently, different ascendant stars—for, here lies the power that controls different fates—why should this be so, when there can be no difference in the times of their conception? Or, if twins conceived at the same moment can have such different fates in regard to the moments of their birth, why cannot others who are born at the same time have equally different fates in regard both to their lives and deaths. After all, the identity of the moment in which they were conceived did not prevent one being born first and the other second. Why, then, if two people are born at the identical time, should anything prevent one from dying first and the other afterwards? If simultaneous conception is compatible with twins having such diverse fortunes in the womb, why should not simultaneous births be compatible with persons having diverse fortunes during their lives on earth? But, if this is so, then all the conclusions (or rather, illusions) of this science go up in smoke.
Let us ask ourselves why it is that those conceived at precisely the same time and under the identical arrangement of the stars have different fates, leading them to be born at different times, yet, persons born of two mothers at precisely the same time and under the same stars may not have different fates leading them of necessity to differences of life and death? Must we answer that when we are conceived we do not yet have our fixed fates, but must wait until we are born? Then, why do the astrologers claim that, if only they knew the hour of individual’s conceptions, their divinations would be much more marvelous? That is why some of them are fond of telling of the philosopher who picked out the precise moment for cohabiting with his wife, so that she might bear him a genius.
So, too, this is why the great astrologer-philosopher, Posidonius, explained the phenomenon of the two twins who became simultaneously sick, by saying that they were both conceived and born at the same time. His point in noting the conception was that it might be argued that they could not be born at precisely the same time, even though it was obvious that they had been conceived together. At all costs, he wanted to link the simultaneous sickness, not to similarity of physical predisposition as the immediate cause, but to the stars.
But, if there is such efficacy in the moment of conception in producing such similarity of fates, like destinies should not be made unlike at birth. Or, if we admit that the destinies of twins are changed because they are born at different times, why should we not admit that the fates had already been changed so that they might be born at different moments. Surely, if the order of being born can change the destiny fixed by conception, then the wills of living persons can change the destiny fixed by birth.
In any case, how does it happen that of twins conceived at precisely the same moment and under the same fate-fixing constellation, one is a boy and the other a girl? I know two such twins, both alive and vigorous in health. They are as alike in looks as a man and a woman can be, but their lives, outwardly and inwardly, are altogether different. Some of the differences may be explained by their sex, as that the one is a staff officer in the army and so practically always away from home, while his sister never leaves her own country and not even her own neighborhood. But, the other differences are inexplicable if one believes in fate, and only become intelligible when one thinks in terms of free will and God’s grace. The brother is a married man with a large family; the sister, a consecrated virgin, who never married.
Nevertheless, people argue, there is much value in a horoscope. Truly, I have already shown, it has no value at all. Or, if it has any value at all, it is only the horoscope taken at birth—if we may believe the astrologers themselves. But, what of the horoscope at the moment of conception? The point here is that there can be only one moment for the conception of twins; nature itself takes care that no woman who is already pregnant can conceive a second time. Yet, they were born with different horoscopes. Ought we to draw the ridiculous conclusion that, while they were being born, either he was turned into a boy or she into a girl?
Another argument of the astrologers is taken from the fact it is not altogether absurd to say that certain sidereal influences bring about different physical phenomena. Thus, we see the changes in the seasons with the coming and going of the sun, and certain kinds of things grow bigger and smaller with the waxing and waning of the moon. This is the case with sea urchins and mussels and with the spring and neap tides. Why, then, they argue, should not human wills be subject to the position of the stars? But, this attempt to link human acts with the stars prompts us to ask why, in regard to our twins, not even their assumptions in regard to bodies seem to be verified.
For instance, what is more pertinent to the body than sex? Yet, under precisely identical stellar influences, twins of diverse sex can be conceived. Think, then, how silly it is to say or believe that the position of the stars, identical for both brother and sister at the moment of conception, could not prevent her from having the same horoscope but a different sex, while the position of the stars at the times when they were born could make the sister so unlike the brother in the practice of virginity.
Augustine of Hippo, The City of God, Books I–VII