A conjunctive adverb is an adverb that has been authorized to perform the function of a conjunction, which simply means that it links one part of a sentence with another. (Standard conjunctions consist of the phrase and clause connectors for, and, nor, but, or, yet, and so, acronymized in that order as the mnemonic FANBOYS.)
However, they are not pure conjunctions, as the FANBOYS words are, and in this role they cannot follow a simple comma; this error is called is a comma splice. Instead, as the examples below demonstrate, conjunctive adverbs—words such as however, otherwise, thus, meanwhile, and hence, when used to express addition, apposition, concession, contrast, reinforcement, result, summary, or time—signal the beginning of an independent clause and must be preceded by a semicolon and followed by a comma. (Alternatively, conjunctive adverbs may appear parenthetically in the middle of the independent clause or may begin or interrupt a separate sentence.)
Each use of a conjunctive adverb below is contrasted with the use of the same word as a simple adverb. Notice that when a word performs the latter function, a semicolon is unnecessary before it (though a comma might be required there to separate two clauses), and no comma must follow it.
However
Adverbial conjunction: “Jones was released last Friday after posting $100,000 bail; however, it was unclear who paid for his release.”
Adverb: “For your sake, however much I abhor that actor, I will go see the movie.”
Otherwise
Adverbial conjunction: “The settlements are an acknowledgment that our business model is sound; otherwise, we would not have agreed to the terms.”
Adverb: “The memory troubled him through the otherwise pleasant afternoon.”
Thus
Adverbial conjunction: “Margins on manufacturing and other businesses have become razor thin; thus, companies must undertake careful analysis of profitability for products and services on a real-time or near real-time basis.”
Adverb: “The enemy struck, and Smith took the bait, thus weakening the left flank of his division.”
Meanwhile
Adverbial conjunction: “Some indicated that they would not respond to the question; meanwhile, others gave their thoughts.”
Adverb: “That’s a good idea for the long term, but meanwhile, we have to address the immediate problem.”
Hence
Adverbial conjunction: “We were preoccupied by the sound of the breaking glass; hence, it is quite possible that somebody planted the gun without being noticed.”
Adverb: “Not too many years hence, the average reader won’t ever have seen a card catalog.”
