No, I'm not mixing them up. Royce indicated there is a difference between we he calls physical matter and energy. I'm just clarifying that space does not require matter (whatever he meant by physical matter, while excluding other forms of energy) for it's existence.Originally posted by heusdens
You're mixing up here two different notions of matter, the philosophical meaning and the physical meaning.
The philosophical meaning of matter includes energy and fields.
Energy is as "physical" as particles (prtons, neutrons, electrons, etc) and fields. And all of these are forms of matter in the philosophical sense.