Another rule of agreement has to do with “delayed subjects.”
For example, when a sentence begins with the word There, the true subject is delayed. The introductory word There is the “grammatical subject.” It is used to begin the sentence, but the”true subject” comes later in the sentence.
There’s a cat on the roof.
The true subject of this sentence is cat. The contraction There’s stands for there is. The sense of the sentence is “A cat is on the roof.”
There are two boys at the front door.
The true subject of this sentence is boys. The phrase “there are” (sometimes spoken as “there’re”) contains a plural verb. The sense of the sentence is “Two boys are at the front door.”
In modern usage, growing numbers of native speakers begin all such sentences with the singular “There’s,” regardless of whether or not the delayed subject is singular or plural:
There’s two boys at the front door.
I believe that the singular grammatical subject used with either singular or plural delayed subjects is going to become the norm in standard spoken English.
However, this usage will continue to be seen as an error of standard usage in written English. Careful writers will avoid it.
REMINDER: Written English is more conservative than spoken English.
