Interjections are one of the eight parts of speech. The words that express sudden feelings or emotions are known as Interjections. Interjection do not specifically cite any one specific emotion or sentiment; they can be used to used to express disgust, enthusiasm, excitement, joy, surprise and several others. As such can be in the form of One Word. Definition of Interjections states "A sudden, short utterance" or "The part of speech that usually expresses emotion and is capable of standing alone". Being standalone, interjections have no connection with the rest of the sentence. They are actually used in quotations, found commonly in dialogue between characters in a book, blogging, texting, writing to friends and other informal letter writing. Interjections are often found or used at the beginning of a sentence but technically they can be anywhere in the sentence, including the middle and the end. Most of the times an interjection with an Exclamation Mark is followed by a sentence with an Exclamation Mark. Adjectives, adverbs, nouns, verbs become interjections when they represent an exclamation. Whilst sticking to grammatical rules for writing, only one exclamation point is necessary to convey the emotion. This is contrary to the novelists or writers who most often use multiple exclamation points, to put more energy in their sentences. Speaking of Writing, Interjections should be avoided in Business Letter Writing as they are not required. Some Interjections are simply sounds like – Ah, Humph, Moo, Mmmm, Oink, Quack, Phew etc. Some Interjections sound weird as they can be new to a reader or listener. English Language itself contains words that are local or used in certain countries, these too, may sound strange to listen or to read. Though there are certain specific words which are considered as Interjections but in a broad sense almost any word can be used as Interjection.
Example – Books are good for knowledge. Books! Treasure house of knowledge.
Interjections don't have that much value in Writing as much as in Speaking. An interjection is generally followed by an Exclamation Mark (!) or a Comma, when written. A Comma is used for a mild emotion; whereas, an exclamation mark is used for abrupt display of surprise, emotion or deep feeling.
Hello! What are doing in this room?
Alas! He is badly injured.
Hurrah! We have won the game.
Oh! What a ball.
Alas, the poet was no more.
Oh, what a wonderful movie!
In the above Interjections Examples, the words in bolds represents Interjection as they express emotions or feelings.