Linguistic Universals and the Category P

I am interested in trying to expand our knowledge regarding the nature of linguistic universals, in particular the relationship of a category P to what is universal to all languages. At some level I am posing the question in (1). (1) Is P part of universal grammar? But (1) presupposes a lot of things, for example that we know what P is and that we know what universal grammar is. So here I want to try to clarify these issues and see if I can come up with a better formulation of the nature of the investigation. First let me try to explain what I mean by universal grammar. If something is universal to all languages, it might be that way for any of several reasons, including the three major types listed in (2), each with two important subtypes. (2) a. Inevitable development due to innate properties of the human brain (i) Language-specific (ii) Not language-specific b. Development triggered by human experienc