Parse the pattern of 'there is/are the noun phrase'

Question

RESULTATIVE PAST. The Present Perfect is also used in reference to a past event to imply that the result of that event is still operative at the present time. This meaning is clearest with ‘transitional event verbs’ (§35B), describing the switch from one state to another. The resultant (and present) state implied by the Perfect is indicated in brackets in these typical examples:

The taxi has arrived (i.e. ‘The taxi is now here’).

She has been given a camera (‘She now has the camera’).

I’ve recovered from my illness (‘I’m now well again’).

In other examples, the resultative implication is still there, even though it is not quite so obvious from the verb’s meaning:

I’ve taken a shower (‘So I’m now clean’).

He’s cut his hand with a knife (‘The cut is still there, i.e. has not yet healed’).

The resultative meaning needs no support from adverbials. It is sometimes difficult to distinguish from the recent indefinite past use (§57): in fact, it is arguably a special case of the recent indefinite past, in which there is the additional resultative inference. One may argue, for instance, that the question Have you seen my trainers? is really a question about the present consequences of seeing the trainers; i.e. ‘Do you know where they are?’

-- Leech, Geoffrey N. 2004. Meaning and the English Verb. Harlow, England: Pearson/Longman.

I'm wondering why it's there is the additional resultative inference, not there is an additional resultative inference.

From time to time, I run across this pattern of 'there is/are the noun', but I have no idea how it's used.

Answer 1

I think you're getting confused by the complexity of your example sentence.

For example, if the sentence were "There is the unicorn I told you about", in a context where the speaker had previously told a friend about a unicorn, which has now appeared, it's obvious that we use the instead of an, because it's the same as "The unicorn I told you about is neighing" (not "A unicorn I told you about is neighing"). And it's equally obvious that we walk in from outside and say out of the blue "There is a unicorn in the garden", because the unicorn was not previously discussed and so is indefinite.

The article follows the same rules after "there is" that it follows in the rest of English. It's far more common to see "there is a" than "there is the" because the "there is" introduces the existence of something, and we frequently need to introduce the existence of something indefinite. There are a few bizarre corner cases like "There is a God" or other phrases where the speaker denies the previously-stated nonexistence of something ("There is a Koosalagoopagoop", "There is a Mongolian Death Worm", etc.) which can be paraphrased as "A God [etc.] does exist". These examples flout the usual rules for articles.

mcalex's answer explains why we need "the" in this particular case.

Answer 2

Because there is only one resultative inference per piece of speech. The author is saying that the Resultant Past form of speech can be identified by its resultative inference. When considering Resultative Past in terms of Recent Indefinite Past, you can think of it as special case (of Recent Indefinite Past) that has the resultative inference (of Resultative Past) added on.

The 'additional' doesn't imply that you could have multiple resultative inferences in a single 'Resultant Past' piece of speech.