See Invisibility (M2, P2, T2, W2)

Level4

You can see any invisible or ethereal objects or beings within your range of vision, as if they were normally visible. Such creatures are visible to you as translucent shapes, allowing you easily to discern the difference between visible and invisible or ethereal creatures.

The spell doesn’t reveal the method used to obtain invisibility, doesn’t reveal illusions or enable you to see through opaque objects, and doesn’t reveal creatures that are simply concealed, hiding, or otherwise hard to see.