Full Idea
Leibniz assigns synthetic a priori status to the principle of sufficient reason, readily conceding that one can deny it without fear of inconsistency.
Gist of Idea
Leibniz said the principle of sufficient reason is synthetic a priori, since its denial is not illogical
Source
report of Gottfried Leibniz (works [1690]) by José A. Benardete - Metaphysics: the logical approach Ch.18
Book Reference
Benardete,José A.: 'Metaphysics: The Logical Approach' [OUP 1989], p.136