There are two observations that inform us about the nature of reality.

One is that mind is always experienced within a body, an object of physical reality. If mind is experienced at any time outside of a body then mind can be said to be undoubtedly as another kind of substance. But since mind is always experienced within a body, mind must rely upon the body for it to be somehow emergent.

The other is that matter (objects) are always experienced together with space and time. Matter experienced without space and time would not be matter but something other than object.