 Discerning the difference between the “reason of being” and the “reason of becoming” is important for understanding the different ways Wolff employs PSR in his exposition of metaphysics. Depending on how exactly “reason” is interpreted, the principle, “nothing is without a sufficient reason for why it is rather than not” may apply either to the realm of possibility or to the realm of actual reality. Toward the end of his Ontologia, Wolff makes an attempt to recognize formally two different versions of PSR as “the Principle of Being” and “the Principle of Becoming” respectively (Ont. §866). As a Principle of Being, PSR stands as a definition of a thing’s essential nature. Yet as a Principle of Becoming, PSR serves to furnish the causes, or grounds, for why a real individual comes into actuality.