The boundaries between word classes are often fuzzy. This book looks at the classification of interjections and similar words of other classes. It reviews work done over the past 250 years on several languages, including English, German, French, Italian, Spanish, Latin, Ancient Greek, Albanian, and Welsh. Most chapters discuss interjections in relation to one of the other traditionally recognized parts of speech: nouns, verbs, adjectives, adverbs, adpositions, and conjunctions. A major focus is on the use of relevant terminology e.g. primary and secondary interjections, proper and improper interjections, and interjectives.

The classification of words in terms of parts of speech is frequently problematic. This book examines the classification of conjunctions and similar words of other classes. It reviews work done from the 19th century to the present on a wide range of languages, including English, German, French, Latin, Ancient Greek, Welsh, Persian, Chinese, Japanese, Ute, and Abun. Most chapters treat conjunctions as opposed to one of the other traditionally recognized parts of speech: nouns, verbs, adjectives, adverbs, adpositions, and interjections. The book's major focus is on the terminology used to describe words on or near the borders between conjunctions and other parts of speech, such as "deverbal conjunctions", "conjunctional adverbs", "prepositional conjunctions", and "so-called conjunctions".