Interjections are the rebels of the grammar world. They don’t play by the usual rules of syntax—they don't need a subject or a verb to function. Instead, they serve as "interruptions" that inject emotion, sentiment, or reaction into language.
Here is a breakdown of how they work and how to handle them.
1. The Function of Interjections
Interjections are primarily used to convey sudden feelings or to grab attention. They are grammatically independent from the rest of the sentence.

Type	Examples	Purpose
Emotive	Wow, Ouch, Yay, Oh	Expresses joy, pain, or surprise.
Cognitive	Uh-huh, Well, Hmm	Indicates thinking or agreement.
Volitive	Shh, Hey, Psst	Used to command or request attention.
Greetings	Hello, Bye, Hi	Social formulas to open/close dialogue.

2. Punctuation Rules
The punctuation you choose depends entirely on the intensity of the emotion you want to convey.
Strong Emotion: Use an exclamation point. This usually stands alone or starts a sentence.
Example: Ouch! That bee just stung me.
Mild Emotion: Use a comma. This keeps the interjection flowing with the rest of the thought.
Example: Oh, I didn't see you standing there.
Uncertainty/Hesitation: Use an ellipsis or a question mark.
Example: Well... I suppose I could help. / Huh? What did you say?
3. Sentence Placement
Interjections are flexible; they can pop up anywhere, though the beginning is most common.
Beginning: "“Hey, watch where you're going!"
Middle (Parenthetical): "The weather, alas, was not in our favor."
End (Question Tags): "That was a pretty great movie, eh?"
4. When to Use (and Avoid) Them
Creative Writing & Speech: Interjections are vital. They make dialogue feel authentic and "human." Without them, characters sound like robots.
Formal/Academic Writing: Generally, avoid them. In a lab report or a legal brief, "Wow, the results were amazing!" sounds unprofessional. You would instead use adverbs or adjectives: "The results were remarkably significant."
A Note on "Primary" vs "Secondary"
Primary Interjections: Words that only exist as interjections (e.g., Oops, Blah, Phew).
Secondary Interjections: Nouns or adjectives used as interjections (e.g., Nonsense! Great! Heavens!).