Conjunctive adverbs, or simply "conjuncts", do exist, and are
different from sentence adverbials.These conjuncts link sentences or paragraphs
and usually appear at the beginning of a sentence.
The adverbials Anonymous mentioned in their first post, those that tell
us something about the verb (why, when, where, how, what for, etc.) are
adjuncts (as opposed to conjuncts. Unlike conjuncts, adjuncts are part of the
structure of the sentence (from the point of view of syntax); they will appear
in the predicate. You also have “sentence adverbials”, which modify an entire
clause or sentence and are placed, usually, at the beginning of the sentence).
Adverb: a part of speech whose main function is that
of modifying a verb, an adjective or another adverb.
Adverbial: a syntactic function that may be
realised by a number of structures (and even single words): adverbs,
prepositional phrases, clauses (both finite and non-finite), noun phrases.
Both conjuncts and adjuncts are adverbials, only they are of different
types.
Most conjuncts are adverbs or prepositional phrases: however,
consequently, yet (meaning ‘however’), firstly, lastly, anyway, nonetheless,
nevertheless, meanwhile, by the way, on the one hand, on the other hand, to
begin with, to sum up, in short, etc. Even some conjunctions can function as
conjuncts, as long as they appear at the very beginning of the sentence (for
example ‘and’ and ‘but’). again, these are not part of either the subject or
the predicate, but remain outside the structure of the sentence and act as
links to the previous sentence/s or paragraph.
Miriam