English interjections tend to be used as independent word-sentences ei­ther in the principal clause, which they make more emotional, or in isolation. Used with the principal clause, interjections occur, as a rule, in pre-position, or – sometimes – in post-position. Used in isolation, an interjection retains its relations with the utterance, since this part of speech is always defined by a situation. Interjections, occurring independently, in isolation, are treated by some grammarians as exclamatory sentences.

If an interjection is part of a principal sentence, it is usually regarded as parenthesis. If it is the case, links within the syntactic structure of the sen­tence are tighter than in sentences, where interjections are used in isolation. In very rare cases, the interjection may become a syntactic nucleus, function­ing in agreement with a noun, e.g. Alas for my hopes! It should be noted that the interjection is always used in pre-position in the sentences of this type.

Thus, the combination of semantic and syntactic features proves that the interjection is undoubtedly a separate independent part of speech. Its Status within the parts-of-speech system is quite peculiar: the interjection may not be treated either as lexical or as functional words, since, strictly speaking, it does not have the property of either. The interjection, however, is characterized by a number of properties, similar to those of modal words and particles. These considerations give some grammarians the ground to suggest that these three parts of speech should be categorized as some third large group, overlapping both with lexical and functional parts of speech.