 Enlightenment thinkers, such as Gottfried Wilhelm Leibniz and Samuel Clarke, reaffirmed the cosmological argument. Leibniz (1646–1716) appealed to a strengthened principle of sufficient reason, according to which “no fact can be real or existing and no statement true without a sufficient reason for its being so and not otherwise” (Monadology, §32). Leibniz uses the principle to argue that the sufficient reason for the “series of things comprehended in the universe of creatures” (§36) must exist outside this series of contingencies and is found in a necessary being that we call God (§38). Samuel Clarke likewise employed the principle of sufficient reason in his cosmological argument (Rowe 1975: chap. 2).