grammaticality - Is "Hello." a sentence?

I've seen this at many places, that people who know very good English (even native speakers of English) write "Hello" followed by a full stop. My confusion is that the use of the full stop indicates that it is a sentence, but a sentence must have a verb in order to be called a sentence.

Hello.

doesn't have any verb in it but has a full stop. So, is it a sentence or not? If it is a sentence, why does it not have a verb in it, which a sentence must have according to the definition of a sentence? If it is not a sentence, why is it ending with a full stop?

Examples That I Have Observed

• Hello. How are you?


• Hello, Johnny.



• Hello? Who is there?

Answer

Is "hello." a sentence?

Yes.

What do you want for dinner?

Vegetable curry.

Hello! You surprised me.

Since you define a sentence as needing a verb, please realize that a sentence does not always have to express its verb. Also note that full stops are necessary in written language only. One does not punctuate spoken sentences the same way we do written sentences.

Additionally, hello is a greeting, which has a special function. When you greet people using spoken English, do you say Hello or do you only say something that has a verb, such as I bring you my greeting, which is hello or perhaps I greet you hello? Do you see what I mean? We don't always speak in fully expressed sentences. And since writing sometimes seeks to copy or represent spoken language, there will be times when something we write does not have an expressed verb, yet it will still be a sentence.

"Hello." is a good example of that. And if you want to know where the verb is, you can consider "hello" to be short for I greet you hello.

Likewise, hello! can also be an exclamation of surprise. See definition 3.

Other exclamations include

Bingo!
Dang!
Hogwash.

To me, these are sentences. If you need a verb for them to be a sentence, you can think of the sentence as

"(I say) 'Hello!'"
"(I say) 'Hogwash'."

The second line of this answer is one word: yes.

I condider "yes" in that context to be a sentence. It is answering the question that is in the first line. If you need a verb for it to be a sentence, you can consider the sentence to be

Yes, I say.

Okay? (Are you "okay" with that?)

Recommended additional reading:

Sentence Well-formedness