I am looking for the reference in Plato about "Soul came into being with the heavens."
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The following quote is a possibility, found in Plato's Laws,Book X, 896.
The soul is the first origin and moving power of all that is, or has become, or will be, and their
contraries.
The trouble is that translations are often very different. I would advise you to read the section starting
around 892 which is the beginning of the discussion between Clinias and the Athenian Stranger about
the nature of the soul and its relation to motion.