Conjunction-words are used alongside of conjunctions to mark subor­dination. Among conjunction-words, there are conjunction-pronouns (who, whoever, what, which) and pronominal adverbs (when, where, why, how, etc.) that combine the properties of a functional part of speech with those of a lexical one. It is subordinate clauses that are introduced by conjunc­tion-words, since a conjunction-word carries out a relative function, i.e. it introduces a pronoun or an adverb into a subordinate clause replacing some of sentence parts: Dan is a friend who has been tested in many ups and downs in my life.

Conjunction-words are adjacent with conjunction adverbs that are treat­ed as distinct from conjunctions proper. Conjunction adverbs (also referred as discourse markers) are however, nevertheless, therefore, accordingly, thus, furthermore, hence, consequently, etc. Contrary to conjunction-pro­nouns and pronominal adverbs, conjunction adverbs function to join parts of compound sentences or independent sentences. The meanings marked by these units are logical, which brings them close to coordinating conjunc­tions rather than to subordinating ones. This property, as well as variation of their location in a sentence proves their peripheral status among conjunc­tion-words. Syntactically, these words function as a parenthesis.

There is a tendency for these words to transform into ordinary coordi­nating conjunctions. The units yet and still are the most advanced in this process: cf. The house was so convenient yet so expensive that Frank could  not afford it even though it was hard for him to turn down the offer. The function to join two homogeneous sentence parts is not typical of conjunc­tion-adverbs, therefore here yet apparently should be classified as a conjunc­tion proper.

Alongside of the described system of connecting linguistic units, rep­resented by the two classes of functional words (prepositions and conjunc­tions) and complemented by conjunction-words, combining properties of functional parts of speech with those of lexical word classes, some scholars suggested a different distribution of connecting elements. According to this point of view, all the mentioned connecting units should be united under the term “connector” that undergo a further subdivision into prepositions, co­ordinating conjunctions and subordinating conjunctions. The fact of uniting all the three groups would underline their similarities and differences.