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One mark of a great mind is the willingness to change it. We can see that in Leonardo. As he wrestled with his earth and water studies during the early 1500s, he ran into evidence that caused him to revise his belief in the microcosm-macrocosm analogy. It was Leonardo at his best, and we have the great fortune of being able to watch that evolution as he wrote the Codex Leicester. There he engaged in a dialogue between theories and experience, and when they conflicted he was receptive to trying a new theory. That willingness to surrender preconceptions was key to his creativity.
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