P1-f: Transitions, parenthetical expressions, etc.
Transitional expressions
Transitional expressions serve as bridges between sentences or parts of sentences. They include conjunctive adverbs such as however, therefore, and moreover and transitional phrases such as for example, as a matter of fact, and in other words. (For complete lists of these expressions, see P3-a.)
When a transitional expression appears between independent clauses in a compound sentence, it is preceded by a semicolon and is usually followed by a comma. (See P3-a.)
When a transitional expression appears at the beginning of a sentence or in the middle of an independent clause, it is usually set off with commas.
exception: If a transitional expression blends smoothly with the rest of the sentence, calling for little or no pause in reading, it does not need to be set off with a comma. Expressions such as also, at least, certainly, consequently, indeed, of course, moreover, no doubt, perhaps, then, and therefore do not always call for a pause.
Alice’s bicycle is broken; therefore you will need to borrow Sue’s.
Parenthetical expressions
Expressions that are distinctly parenthetical, providing only supplemental information, should be set off with commas. They interrupt the flow of a sentence or appear at the end as afterthoughts.
Absolute phrases
An absolute phrase, which modifies the whole sentence, usually consists of a noun followed by a participle or participial phrase. (See B3-d.) Absolute phrases may appear at the beginning or at the end of a sentence and should be set off with commas.
note: Do not insert a comma between the noun and the participle in an absolute construction.
Word groups expressing contrast
Sharp contrasts beginning with words such as not, never, and unlike are set off with commas.
