An existential clause, such as There was an old person of Dover, functions to “represent that something exists or happens…The word there in such clauses is neither a participant nor a circumstance – it has no representational function in the transitivity structure of the clause; but it serves to indicate the feature of existence, and it is needed interpersonally as a Subject” (H & M, p.257). The second part of the clause, the “entity or event which is being said to exist” (H & M, p.258) is labelled the Existent.
Students may often confuse the existential ‘there’ with the circumstantial ‘there’. A good example from H & M (p.258) is to compare There’s your father on the line (existential) with There’s your father (circumstantial relational). Note that the response to the first is Oh, is there? while that for the second is Oh, is he?
The existential clause itself, however, may contain “a distinct circumstantial element of time or place” (H & M, p.258) in which, if thematic, the Subject there may be omitted, such as On the wall (there) was a Picasso painting, but will appear in the response Oh, is there? This circumstantial element may also be reflected in the choice of verb as Process, which is not necessarily be but may almost merge into the material, such as On the wall (there) hangs a Picasso painting. This may also be followed by a non-finite clause as a “way of ‘locating’ the process in space-time” (H & M, p.258):
There stood G. F. Westerby, looking pleased with
himself, staring out over the decades (BNC)