 Since a Cartesian substance is a thing that is ontologically independent (Principles I.51–52), a complete thing is an ontologically independent thing. When we clearly and distinctly perceive mind and body to be complete, we know that they are substances. When we still clearly and distinctly perceive them to be substances after clearly and distinctly perceiving them apart from each other, we know that they are not the same substance under different descriptions. On this view, Descartes holds that mind and body are ontologically independent substances, and their distinctness consists in their ability to continue to exist even after God separates  them.[36]