Is a subject always noun?

No, a subject is not always a noun. While nouns are the most common type of subject, other parts of speech can also function as subjects.

Here's why:

* Pronouns: Pronouns can act as subjects, replacing nouns. For example: "She went to the store."

* Gerunds: Gerunds are verb forms ending in "-ing" that act as nouns. For example: "Swimming is my favorite activity."

* Infinitives: Infinitives (the "to" form of verbs) can act as subjects. For example: "To learn is a lifelong process."

* Clauses: Entire clauses can function as subjects. For example: "What you said made me think."

In essence, a subject is the part of a sentence that performs the action of the verb. The subject can be a noun, pronoun, gerund, infinitive, or clause.