Here's why:
* Abstract Noun: An abstract noun refers to a concept, idea, feeling, quality, or state that cannot be touched or seen.
* "When" as an Abstract Noun: "When" can represent the concept of time or a specific point in time. Time itself is an abstract concept.
Example:
* "The doctor will arrive in the morning." In this sentence, "morning" functions as an abstract noun, representing a specific point in time.
Other Examples:
* "The meeting will be held at a later date." ("Date" is an abstract noun representing a specific point in time.)
* "He remembers the time when he first met her." ("Time" is an abstract noun representing the general concept of time.)
Important Note: "When" can also be a conjunction, an adverb, or an interrogative word. Its function depends on the context of the sentence.