1. Notional and Formal
2. a) Notional: Personal and Non-personal
b) Formal: Impersonal and Introductory
3. Introductory: It-subject and There-subject
I don't use the term 'preparatory' but I guess it's the same as 'introductory'.
Impersonal is different from introductory. I illustrated this difference in my post above in this thread.
We can further speak on the difference between introductory it-subject and introductory there-subject.
OK. So, there is a man over there is an example of an introductory subject, a.k.a. expletive, empty subject, preparatory subject, right?
Let's go back to impersonal subjects. How does the following (common) argument sit with you? It is raining = The weather is raining.
I think these are totally different structures. This substitution is totally artificial. 'It' is called impersonal because it suggets that there can be no doer of the action. How would you interprete then other impersonal sentences: 'It is summer' or 'It is me' or 'It is time'?