In grammar, an interjection or exclamation is a word used to express a particular emotion or sentiment on the part of the speaker (although most interjections have clear definitions). Filled pauses such as uh, er, um are also considered interjections. Interjections are often placed at the beginning of a sentence.
An interjection is sometimes expressed as a single word or non-sentence phrase, followed by a punctuation mark. The isolated usage of an interjection does not represent a complete sentence in conventional English writing. Thus, in formal writing, the interjection will be incorporated into a larger sentence clause.
Interjection as a figure of speech refers to the use of one word. For example, lawyers in the United States of America traditionally say: Objection! or soldiers: Fire!.
Conventions like Hi, Bye and Goodbye are interjections, as are exclamations like Cheers! and Hooray!. They are very often characterized by exclamation marks depending on the stress of the attitude or the force of the emotion they are expressing. Well (a short form of "that is well") can also be used as an interjection: "Well! That's great!" or "Well, don't worry." Much profanity takes the form of interjections. Some linguists consider the pro-sentences yes, no, amen and okay as interjections, since they have no syntactical connection with other words and rather work as sentences themselves. Expressions such as "Excuse me!", "Sorry!", "No thank you!", "Oh dear!", "Hey that's mine!", and similar ones often serve as interjections. Interjections can be phrases or even sentences, as well as words, such as "Oh!" "Pooh!" "Wow!" or "sup!".
Several English interjections contain sounds, or are sounds as opposed to words, that do not (or very rarely) exist in regular English phonological inventory. For example:
Ahem[əʔəm], [ʔəʔəm], [əɦəm], or [ʔəhəm], ("attention!") may contain a glottal stop[ʔ] or a [ɦ] in any dialect of English; the glottal stop is common in American English, some British dialects, and in other languages, such as German.
Gah[ɡæh], [ɡɑː] ("Gah, there's nothing to do!") ends with [h], which does not occur with regular English words.
Oops, an interjection made in response to the observation of a minor mistake, usually written as "Oops!" or "Whoops!"
Psst[psː] ("here!"), is another entirely consonantal syllable-word, and its consonant cluster does not occur initially in regular English words.
Shh[ʃːː] ("quiet!") is an entirely consonantal syllable.
Tut-tut[ǀ ǀ] ("shame..."), also spelled tsk-tsk, is made up entirely of clicks, which are an active part of regular speech in several African languages. This particular click is dental. (This also has the spelling pronunciation [tʌt tʌt].)
Ugh[ʌx] ("disgusting!") ends with a velar fricative consonant, which is otherwise restricted to just a few regional dialects of English, though is common in languages like Spanish, German, Gaelic and Russian.
Whew or phew[ɸɪu], ɸju ("what a relief!"), also spelled shew, may start with a bilabial fricative, a sound pronounced with a strong puff of air through the lips. This sound is a common phoneme in such languages as Suki (a language of New Guinea) and Ewe and Logba (both spoken in Ghana).
Yeah[jɛ(ə)] ("yes") ends with the short vowel [ɛ], or in some dialects [æ] or tensed [ɛə], neither of which are found at the end of any regular English words.
Drawing on earlier writings by Wilhelm Wundt, interjections may be subdivided into primary and secondary interjections.
primary interjections do not belong to and are not derived from any word category and also encompass onomatopoeia. Presumably, they originate from animal or human noises. Examples: Oops., Ouch!
secondary interjections in contrast are words with another meaning, most often substantives. However, as an interjection they are used by themselves and express mental attitudes or states. Examples: Damn!, Hell!