(linguistics) A part of speech that has no inherent lexical definition but must be associated with another word to impart meaning, often a grammatical category: for example, the English word to in a full infinitive phrase (to eat) or O in a vocative phrase (O Canada), or as a discourse marker (mmm).

In English there is no grammatical device to differentiate predicational judgments from nonpredicational descriptions. This distinction does cast a shadow on the grammatical sphere to some extent, but recognition of it must generally be made in semantic terms. It is maintained here that in Japanese, on the other hand, the distinction is grammatically realized through the use of the two particles wa and ga.

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(linguistics) A part of speech which cannot be inflected.

322. The parts of speech which are neither declined nor conjugated, are called by the general name of particles. 323. They are adverbs, prepositions, conjunctions, and interjections.

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