Bardaisan sets out to demonstrate that human beings, notwithstanding their being in many respects at the mercy of forces over which they have no control, nevertheless have a free will and can choose between right and wrong actions. Bardaisan does not contribute anything substantial to the perennial argument about freedom and necessity, but to the modern reader the astrological detail in which he writes is likely to be engaging. Under the heading of necessity he finds two factors, Nature and Fate, and identifies the second with the influence of the stars and planets. In the Dialogue , Bardaisan is well aware of criticism that he is basically an astrologer. He admits that he once cherished the arts of the Chaldeans, but insists he no longer does so.
Fate determines whether one is rich or poor, well or ill, has a large family or is childless.
But Fate has its limits. Nature, not Fate, determines that a man cannot become a father before he is fifteen, or a woman a mother before she is thirteen. It is Nature that causes men and women to unite and bear children. But it is Fate that makes marriages go sour and taints the working of Nature with impure passions. A conjunction of Mercury with Venus, in the house of Mercury, gives rise to sculptors, painters, and money-changers, or, in the house of Venus, to dancers, singers, and poets.