This entails that it is a non-inflecting word which has the distribution of a sentence but is not an ideophone. An interjection conveys the speaker's reaction to something in the speech situation or in the universe of discourse. The prototypical interjection is monomorphematic, like Ouch! Secondarily, morphologically or even syntactically complex lexemes like Really!? or Good heavens! count as interjections.

Interjections classify by structural and semantic criteria:

A structural division is as follows:
• A primary interjection is one lacking syntactic structure (although it may be morphologically complex).
• A secondary interjection is a sentence or phrase which has phraseological status in the system and is used like a holophrastic utterance.

A discourse-functional division is as follows:
• A deictic interjection conveys a – typically emotional – reaction to something in the speech situation.
• An anaphoric interjection conveys a reaction to something said before.

This produces the following cross-classification: