Transitional expressions serve as bridges between sentences or parts of sentences. They include conjunctive adverbs and transitional phrases.
Transitional expression between independent clauses
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.
Transitional expression at the beginning or within a sentence
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.
Transitions without commas
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 commas. Expressions such as also, at least, certainly, consequently, indeed, of course, no doubt, perhaps, then, and therefore do not always call for a pause.
Transitional expressions
Exercises:
Major uses of the comma 1
Major uses of the comma 2
All uses of the comma