Chapter 10

20 Those who say that future events are unalterable and that a truth about the future cannot turn into a falsehood do not establish the necessity of fate; they explain the force of words. But those who introduce an everlasting chain of causes strip the human mind of free will and bind it in the necessity of fate.

Enough of this; let us consider something else. Chrysippus argues as follows: “If there is motion without a cause, not every statement—what dialecticians call a ‘proposition’—will be either true or false; for whatever has no efficient causes will be neither true nor false. But every statement is either true or false. Therefore there is no motion without a cause. If that is so, everything that happens happens through antecedent causes. If that is so, everything happens by fate. It follows, then, that whatever happens happens by fate.”

21 Here, to begin with, if I chose to agree with Epicurus and deny that every statement is either true or false, I would rather take that blow than endorse the view that everything happens by fate. The former position at least admits of argument; the latter is intolerable. And so Chrysippus strains every nerve to persuade us that every proposition is either true or false. For Epicurus fears that, if he concedes this, he must concede that whatever happens happens by fate. He thinks that if one of two alternatives has been true from eternity, it is also certain, and if certain, necessary; in this way, he thinks, both necessity and fate are established. In just the same way, Chrysippus fears that, unless he secures the principle that every statement is either true or false, he cannot maintain that everything happens by fate and through eternal causes of future events.

22 But Epicurus thinks the necessity of fate can be avoided by the atom's swerve. Thus, besides motion from weight and from a blow, a third kind of motion arises, when an atom swerves by the smallest interval—what he calls “the minimum.” That this swerve occurs without a cause he is compelled to admit in substance, if not in words. For an atom does not swerve because another atom strikes it. How can one be struck by another if, as Epicurus holds, the indivisible bodies are carried by their weight perpendicularly downward in straight lines? It follows that, if one is never driven aside by another, neither does one ever touch another. From this it follows that, even if an atom exists and swerves, it swerves without a cause.

20 To say that future events cannot change, or that something true about the future cannot become false, does not establish necessary fate. It explains what words mean. Introducing an endless chain of causes is different. That takes free choice from the human mind and ties it to fate's necessity.

Enough on that subject. Let us look at another. Chrysippus reasons this way: suppose some movement has no cause. Then some statements—“propositions,” as logicians call them—will have no truth or falsity. Anything lacking causes that produce it would lack truth or falsity. But truth or falsity belongs to every statement. Therefore, movement with no cause does not occur. On that basis, earlier causes bring about every event. If that holds, fate brings about every event. So whatever takes place does so through fate.

21 My first response is this. I could side with Epicurus and deny that truth or falsity must belong to every statement. I would sooner take that hit than accept fate for everything. Epicurus's view at least leaves room for debate. The other view cannot be tolerated. Chrysippus therefore puts all his strength into persuading us that a proposition must be true or false. Epicurus fears that accepting this would force him to accept that fate governs all events. His reasoning is that one alternative's having been true forever makes it certain; certainty makes it necessary. He thinks that establishes both necessity and fate. Chrysippus has the opposite fear. Without establishing truth or falsity for every assertion, he fears he cannot maintain that fate, and eternal causes of future events, govern everything.

22 Epicurus thinks an atom's change of course lets him avoid fate's necessity. Weight and impact already produce two kinds of movement. Now he adds a third: an atom shifts sideways by the smallest distance, which he calls “the minimum.” Whether he admits it in words or not, he has to admit in substance that this sideways shift has no cause. No collision with another atom makes it turn aside. On his theory, indivisible bodies move straight downward under their own weight. How, then, could one hit another? If none ever knocks another aside, none even comes into contact with another. That shows that even if atoms exist and turn aside, they do so without a cause.