If matter isn't substantial then what is meant by substantial?
Asking what matter is, is a bit like asking where the Eiffel Tower is. The answer to the question gives a relative not an absolute. We only understand where things are relative to where other things are, there is no such thing as an absolute position. Where am I? Or do I really mean where is everything else?
What is the nature of matter? I think the question assumes the need for a relation ie. how we are interested in relating the subject of the question to other things. The answer might involve pointing out that the physics of matter does not paint a picture like our everyday picture of matter, we can understand particles as waves and matter as energy etc. The answer does not do away with the everyday picture anymore than pointing out that the Eiffel Tower is not located at a particular point in space does away with the idea that the Eiffel Tower is in Paris.
The problem with seeing matter as information or probability is that you have reduced it to mathematical abstraction. Again compare with 'where is...' type of question - you can't reduce that sort of question completely to a mathematical abstraction, try it if you don't believe me. I think the temptation to do this in fundamental physics is because it is hard to make sense of quantum mechanics except as a mathematical abstraction, but that's just the trickiness of the terrain.
