I created my own goals, which, together with my studies in mathematics, has given me an excellent foundation for this program.
The phrase "together with my studies in mathematics" is parenthetical (we could put it in brackets, for example). It is not grammatically integrated into the sentence. It is not, therefore, part of the subject of the verb "has".
The verb "has" is the main verb in the relative clause "which has given me an excellent foundation for this program". We interpret the Subject of this clause, the word "which", through its antecedent. Its antcedent, however, is not the plural phrase "my own goals". Rather, it is the clause "I created my own goals". Clauses take singular verb agreement in English. Consider:
- He licks his fingers, which really anoys me.
It is not the fingers which annoy the speaker, it is the whole situation that "He licks his fingers".
The Original Poster is correct, and his critic wrong. The verb has is singular because the clause "I created my own goals" is the antecedent for the Subject, not the plural noun phrase "my own goals".
It is the experience of creating his own goals which has provided the Original Poster with a good foundation for his program - not the goals themselves.
Best Answer
The subject is "earthquake." That is the entire subject. As such, the sentence would be written:
"Along with its subsequent aftershocks" is a prepositional phrase. A prepositional phrase is never part of a subject. It does not affect the count of the subject. Whatever is said in a prepositional phrase, no matter how plural it may be, does not make a singular subject plural.
The only thing that can make an otherwise singular subject plural is the conjunction "and." If the word "and" were used instead of "along with," then the verb would be "have."
Here is a link that explains all of this in more detail:
http://www.chompchomp.com/terms/subject.htm