  Mental states are characterised by two main properties, subjectivity, otherwise known as privileged access, and intentionality. Physical objects and their properties are sometimes observable and sometimes not, but any physical object is equally accessible, in principle, to anyone. From the right location, we could all see the tree in the quad, and, though none of us can observe an electron directly, everyone is equally capable of detecting it in the same ways using instruments. But the possessor of mental states has a privileged access to them that no-one else can share. That is why there is a sceptical ‘problem of other minds’, but no corresponding ‘problem of my own mind’. This suggests to some philosophers that minds are not ordinary occupants of physical space.