Here's why:
* Subject: The subject of a sentence is the person, place, or thing that performs the action. It's essential for understanding the meaning of the sentence. While you can sometimes infer the subject from context, it's technically always present, even if not explicitly stated.
Example:
* Explicit: "The cat sat on the mat." (Subject: "The cat")
* Implied: "Sat on the mat." (Subject: implied to be "the cat" based on context)
* Other sentence parts: Other parts of a sentence, like the verb, object, or prepositional phrase, cannot be implied. If they are missing, the sentence becomes grammatically incorrect or ambiguous.
Example:
* Incorrect: "Ran quickly." (Missing subject and object)
* Ambiguous: "To the store." (Missing subject and verb)
Therefore, only the subject can be implied in English sentences, and even then, it's often inferred based on context rather than truly omitted.