Ancient History Encyclopedia. Retrieved 2 May 2017. ↑ "Principles of Nature and Grace", 1714, Article 7. ↑ Martin Heidegger, Introduction to Metaphysics, Yale University Press, New Haven and London (1959), pp. 7–8. ↑ "The Fundamental Question". www.hedweb.com. Retrieved 26 April 2017. ↑ Geier, Manfred.