 Here Spinoza writes as if a body's essence and its form are one and the same. In each of PIl4, 5 and 6, Spinoza speaks of bodily persistence in terms of its parts keeping the same ratio of motion and rest. If the parts do so, the body, says Spinoza “will retain its nature, as before, with no change of form” (emphasis added). PIl7 also speaks of a body's retaining its “nature”, despite change. These are plainly meant to state conditions on individual persistence. These lemmas seem to equate nature and form. So by transitivity of identity, form=nature=essence. Moreover, Spinoza implies that so long as this form or essence is retained, a thing is not destroyed. “Form”, “nature” and “essence” than, refer to something in virtue of the persistence of which an individual retains its identity.