Here's why:
* Noun: "Summer" is a noun, representing a season of the year.
* Determiner: "This" is a determiner, modifying the noun "summer" to specify a particular summer.
* Phrase: When combined, "this" and "summer" form a noun phrase that functions as a subject or object within a sentence.
For example:
* This summer was incredibly hot. (Subject of the sentence)
* We went on a trip this summer. (Object of the verb "went")