Expletive 'there' originates DP-internally as an instance of deictic 'there'
(as in non-standard 'that there book'), with this assimilation related to the language faculty’s frowning on accidental homophony within the functional domain. The definiteness effect, which is induced by expletive 'there' or counterparts of it, including silent ones, results from a blocking effect, probably not specific to existential sentences, that certain determiners such as 'the' impose on the movement of expletive 'there' from its DP-internal position up to a sentential subject position. This account of the definiteness effect depends on the DP-internal origin of expletive 'there'. The fact that an expletive 'there' in subject position is cross-linguistically rare may be due to the movement of
expletive 'there' to subject position being an instance of preposition-stranding