Which part of speech cannot stand alone and usually links words together in a sentence?

The part of speech that cannot stand alone and typically links words, phrases, or clauses together in a sentence is a conjunction. Conjunctions serve the essential function of connecting ideas and establishing relationships between different parts of a sentence. For instance, in the sentence "I want to go to the park, but it is raining," the conjunction "but" links two independent clauses, highlighting a contrast between the speaker's desire and the weather condition.

In contrast, adjectives and adverbs serve to modify nouns and verbs, respectively, providing more detail but not functioning as connectors within a sentence structure. Interjections express emotions or exclamations but do not connect parts of sentences; they usually stand alone, conveying feelings or reactions without grammatical linkage.