Combining Texts

You have chosen 'Letters to a German Princess' by Leonhard Euler, 'Philosophy' by Karl Jaspers and 'On the Principles of Indiscernibles' by Gottfried Leibniz

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All the ideas for Natural Theory, or select a subheading:
      A. Speculations on Nature
      B. Natural Kinds
      C. Causation
      D. Laws of Nature