Why Does Water Move Through a River?
A philosophical inquiry into the cause of the motion of river water
A full page of red-chalk mirror-script with no diagram, given over to a reasoned question about the cause of water's motion. Leonardo argues that river water is either called, or driven, or moves of itself, then interrogates each option: who summons it, who drives it, and whether self-motion would imply reason. He concludes that bodies of continually changing form cannot possess reason, for in them there is no judgment.
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Is river water called, driven, or self-moving?
The passage sets out three possibilities for the motion of river water: that it is called, that it is driven, or that it moves of itself. Each is pressed with a question - who summons it, who drives it - as a way of probing the true cause of a river's flow.
Motion and the absence of judgment in changing bodies
Leonardo reasons that if water moved of itself it would show that it possesses reason. But a body in continual change of form cannot have reason, because such a body has no judgment, so its motion must be caused from without.