I mentioned Samuel Alexander last week in the course of discussing the semantics of emergence.
At one time, I considered Alexander to be an important and impressive philosopher. I'm afraid I've outgrown his appeal, but he is certainly worth a blog entry of his own.
He is the author of Space, Time, and Deity (1920). If you are interested in the social history of academe, you might also want to know that he was the first Jewish fellow of an Oxbridge college.
The book named above is one of the early expressions of metaphysicians' efforts to incorporate Einsteinian physics into their own speculations. Space and Time are named separately in the title, but the book is suffused with the idea that they are one, and that this one thing, spacetime, is not merely (as many philosophers have thought and still think) a matter of relationships among objects or events, it is a directly intuited substance.
What is more, spacetime is THE substance for Alexander. Over the course of the book it becomes clear that spacetime is substance itself. Matter consists simply of the properties of spacetime, life is an emergent from matter, mind from life, and deity will in time emerge from, is even now in the process of emerging, from mind. All of these levels of reality are spacetime, though none of them are "nothing but" spacetime. Emergentism is distinct from reductionism.
Alexander has been said to have combined in an idiosyncratic way both of the great philosophical "tides" affecting the British isles a century ago, the outgoing tide of Hegelian idealism and the incoming tide of realism, conceived of as naturalism.
I outgrew my own Alexander phase as I came to see the ambiguities in the word "emergence," and grew dissatisfied with the magic I was allowing the word to perform on my behalf.
At any rate, the Stanford Encyclopedia of Philosophy has a good write-up.