[*] 213. Adverbs, Prepositions, Conjunctions, and Interjections are called Particles.
In their origin Adverbs, Prepositions, and Conjunctions are either (1) case-forms, actual or extinct, or (2) compounds and phrases.
Particles cannot always be distinctly classified, for many adverbs are used also as prepositions and many as conjunctions (ยงยง 219 and 222).