To Florus 5.47

But what they experience as they go on does not always come from necessity: much comes from possibility. This can be seen in every body, though it would require a longer discussion. Let us give a few examples. Bodies by nature grow together through combination and break apart through division. Those subject to destruction are therefore capable of injury. Their capacity to be wounded comes from necessity; their actually being wounded comes from possibility. Thus the nature of a possibility comes from necessity, although the realization of that possibility is not necessary. For example, a horse, an ox, and similar living creatures have a vulnerable nature, and necessarily possess the capacity for harm. Yet it is not always necessary that they be wounded. If their keepers’ care protects them from blows, they can remain unwounded; if they are not guarded, they can also be wounded. There is therefore a great difference between what arises from possibility and what arises from necessity. Unless this distinction is preserved, countless errors follow.

To make this clear by comparison: some opponents of medicine went astray, arguing that this art has no usefulness. They argue as follows: ‘Does medicine help those who will die or those who will live? If those who will die, it accomplishes nothing; if those who will live, its effort is pointless. Those who were going to die will die despite its labor; those who were going to live could have remained safe without its benefit.’ What a neat and polished conclusion! But medicine’s defenders dissolve it as follows: ‘This art helps neither those who will live nor those who will die by necessity, but those for whom either outcome is possible. Medicine does not help someone who will undoubtedly die, because it cannot make him immortal. Nor does it assist someone who will undoubtedly remain unharmed. It assists someone who can be in danger if untreated, but can be rescued if treated.’ Thus, just as the trained art cannot help someone destined to live or die by necessity, it can help those who may live or die as a matter of possibility. Those earlier critics of medical effort therefore closed with necessity an argument begun from possibility. This form of argument extends to countless matters.

For example, the law forbids homicide. It also forbids providing an occasion of negligence through which people fall into danger, as with a goring bull (Exodus 21:28–32) and the parapets of houses (Deuteronomy 22:8). Someone can say: ‘Does this care help a person who will live or one who will die? If one who will die, it accomplishes nothing; if one who will live, it takes needless precautions’—if these opposite outcomes necessarily follow whether obstacles are present or not. But that is false. Mortals are most rightly protected so that, through the resources of care, they escape what they could have suffered without care. What comes from possibility is therefore one thing; what comes from necessity is another.

Let us now show how these preliminaries help us. God made a human being with free will and a good nature, but one capable of virtues he could acquire for himself through a mind possessing its own freedom. This free will could not stand otherwise than by possessing also the possibility of sinning. A person therefore possesses freedom necessarily, while a particular act of will arises as a possibility. He cannot fail to be free, but cannot be compelled toward either will. A possible effect is thus produced by something necessary. In the possible sphere one can sin; in the necessary sphere one cannot. In the necessary sphere, the one assessed is not the actor but the creator himself: whatever the human being is capable of comes wholly from God. In the possible sphere, however, the actor himself is weighed.