Sentence:  <WSD>Protomatter</WSD> is a potential for existence that requires the creative act of a substantial form to bring a particular substance into existence. In other words, although <WSD>protomatter</WSD> could exist as any particular substance, substantial form constrains <WSD>protomatter</WSD> into a particular substance. 
Meaning of the word marked with <WSD> tags:  The ultimate basis of physical substance, before it has been given form.