Famously, in the years of the Discours de Métaphysique Leibniz derives the principle of the identity of indiscernibles from his theory of complete concepts. Almost equally famously, in the correspondence with Clarke he deduces the principle from the validity of the principle of sufficient reason for the actions of God. However, in addition to these "top-down" strategies there is also (relatively neglected by commentators) a "bottom-up" strategy of arguing for the PII. This third strategy can be found at various places in the Nouveaux Essais and in parallel passages from the correspondence with De Volder. There, Leibniz develops what could be called a "perspectivity argument" for the PII according to which because of the perspectivity inherent in the petites perceptions of an individual substance no two substances can be perfectly alike. This way of arguing for the PII can be already found in the De Summa Rerum, where it complements the deduction of the PII from theological principles.

In the Nouveaux Essais, this "bottom-up" strategy of arguing for the PII plays an important role in Leibniz’s discussion of the possibility of twin-consciousnesses in other actual worlds. Even if indistinguishable conscious states of different individual substances are conceivable at any given point of time, Leibniz argues there, due to the perspectivity of the petites perceptions of each conscious mind an indistinguishable diachronic development of conscious states is inconceivable. In his view, this is also what excludes the possibility of Locke’s thought experiment of the divine transfer of a consciousness from one substance to another without any noticeable difference. Because the "bottom-up" strategy of arguing for the PII starts with a description of the structure of perception, this strategy thus contributes to what makes Leibniz’s view of the identity of individual substances part of a "descriptive metaphysics".