Full Idea
The importance of the field concept (as ultimate) is that it allows us to escape from the apparently pervasive concepts of substance and its properties. A field has no substance other than its powers (or its potentials).
Gist of Idea
We can escape substance and its properties, if we take fields of pure powers as ultimate
Source
Harré,R./Madden,E.H. (Causal Powers [1975], 8.VII)
Book Reference
Harré,R/Madden,E.H.: 'Causal Powers: A Theory of Natural Necessity' [Blackwell 1975], p.155
A Reaction
You can't run away from substance by only thinking about what is ultimate. Are they going to ignore separate objects? What gives them identity? Do they have any properties? What has the properties? More work needed here.