In Meditation II, Descartes discusses the nature of body via the piece of wax example.
Consider a piece of wax in its room temperature state: honey-like smell, rigid, and cool to the touch. If the wax is heated up, its properties changes: no smell, different, liquid-like, and hot to the touch. It happens that everything observed in the room temperature state are not permanent, without which the piece of wax can still exist.
Descartes argue that the only property that the wax (and all other substances) absolutely needs to exist is extension, which is the property that it occupies three dimensional space. Unlike Locke’s solidity, Descartes’s idea of extension does not rely on human sensory experience. Yet it faces some plausible objections:
- A span of empty space does not constitute a body.
- Space without physical impenetrability cannot be considered a body.