In the following sentence how many persons are mentioned, 3 or 4?
The Sentence is:
"They invited me to dinner, and when I arrived at their house, there stood my girlfriend's father, and her mother, Katherine the school principal, and Tommy."
First interpretation (4 persons):
The two and makes that this sentence talks about 2 pairs of persons (4 persons in total).
1- my girlfriend's father
and
2- her mother
3- Katherine the school principal
and
4- Tommy
This is, separating first couple in father and mother and the other couple Katherine and Tommy.
Second interpretation (3 persons):
If I follow the rules of how/when to use commas, I find 3 persons here.
1- my girlfriend's father
and
2- her mother, Katherine the school principal
and
3- Tommy
In this case Katherine the school principal that appears after the comma is an additional information about the second person that is her mother
UPDATE:
The main rules of commas used in this sentence suggests to be these 3 persons.
Use a comma before any coordinating conjunction (and, but, for, or, nor, so, yet) that links two independent clauses
Use a comma after a dependent clause that starts a sentence
Use commas to offset appositives from the rest of the sentence
Appositives act as synonyms for a juxtaposed word or phrase. For example, "While running, I saw a mallard, a kind of duck." "A kind of duck" is the appositive, which gives more information about "a mallard."
If the appositive occurs in the middle of the sentence, both sides of the phrase need a comma, as in:
A mallard, a kind of duck, attacked me.
References: