Sentence:  Rephrasing Heisenberg's solution, one could say that the explanation of massive, kinetic, and electromagnetic phenomena, all of which may be regarded as real, requires some underlying substrate or ultimate matter or <WSD>protomatter</WSD> that itself is real but only in a potential way. 
Meaning of the word marked with <WSD> tags:  The ultimate basis of physical substance, before it has been given form.