In the Phaedo at 96a-101c, Plato appears to be committed to the following three negative principles of causation: (1) the same cause cannot produce opposite effects; (2) opposite causes cannot produce the same effect; (3) an opposite cannot cause an opposite. Plato also appears to hold a further, positive causal principle, the principle that (4) like causes like. Scholars have often been puzzled by or critical of Plato’s commitment to these principles. In this thesis, I try to gain a better understanding of the principles and of why Plato may have found them so compelling. I begin by providing a broader context for Plato’s negative causal principles (principles 1-3). I show that Plato was by no means alone among ancient philosophers in assuming that the same cause cannot produce opposite effects, that opposite causes cannot produce the same effect, and that an opposite cannot cause an opposite. We can trace these assumptions back before Plato to Presocratic philosophy and forward to the Aristotelian or Peripatetic tradition, and even beyond. The assumptions had a deep and far-reaching influence on ancient thought beyond Plato’s dialogues, and so we should not be surprised if Plato has no difficulty invoking them in the Phaedo. Next, I turn directly to Plato’s use of his principles of causation in the Phaedo. There, the negative causal principles (principles 1-3) give rise to a series of puzzles that Socrates says he encountered when, as a young man, he engaged with the study of physics. The puzzles lead Socrates to abandon physics, and to adopt instead a special version of the principle that like causes like (principle 4). Scholars often accuse Plato of relying on arguments that are silly or sophistic in this part of the Phaedo. I try to show that Plato’s approach is more plausible and engaging than it first appears. Central to my argument is the suggestion that, for Plato, a real cause of anything being F is a stable and absolute cause of being F. In my final chapter, I focus on a passage in the Cratylus (393b-394e), where Plato says that humans beget humans, horses beget horses, and so on. Ademollo, in his commentary on the Cratylus, says that these are instances of the like-causes-like principle (principle 4). Plato also claims that a king begets a king, a good father begets a good son, a good-looking father begets a good-looking son, and so on. But Ademollo insists that we are not meant to take these further cases seriously. I argue that Ademollo is wrong about the Cratylus passage. Plato really does think that a king begets a king, a good father begets a good son, and so on. But I also draw on my earlier discussion to argue that humans and other mortal creatures cannot ultimately be real causes of their offspring for Plato, and so cannot be genuine instances of like causing like.
Ancient philosophy, Plato, causes, causation, Phaedo, Presocratics, Hippocratics, Peripatetics, Problemata, Cratylus, fathers and sons, Timaeus, demiurge, like causes like, aporia
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