Combining Texts

You have chosen 'Treatise on double arguments' by Anon (Diss), 'Confessio naturae contra atheistas' by Gottfried Leibniz and 'Boole calculus and the Concept script' by Gottlob Frege

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All the ideas for Modality, or select a subheading:
      A. Necessity
      B. Possibility
      C. Sources of Modality
      D. Knowledge of Modality
      E. Possible worlds