Adverbs and short phrases, _when they break the connection_, should be between commas. Some of the most common words and phrases so used are the following: Also, too, there, indeed, perhaps, surely, moreover, likewise, however, finally, namely, therefore, apparently, meanwhile, consequently, unquestionably, accordingly, notwithstanding, in truth, in fact, in short, in general, in reality, no doubt, of course, as it were, at all events, to be brief, to be sure, now and then, on the contrary, in a word, by chance, in that case, in the mean time, for the most part. "History, in a word, is replete with moral lessons." "As an orator, however, he was not great." "There is, remember, a limit at which forbearance ceases to be a virtue." "Our civilization, therefore, is not an unmixed good." "This, I grant you, is not of great importance."
If, however, the adverb does not break the connection, but readily coalesces with the rest of the sentence, the commas are omitted. "Morning will come at last, however dark the night may be." "We then proceeded on our way." "Our civilization is therefore not an unmixed good." "Patience, I say; your mind perhaps may change."
Adverbial phrases and clauses beginning a sentence are set off by commas. "In truth, I could not tell." "To sum up, the matter is this." "Everything being ready, they set out." "By looking a little deeper, the reason will be found." "Finally, let me sum up the argument." "If the premises were admitted, I should deny the conclusion." "Where your treasure is, there will your heart be also."
Words used in apposition should be isolated by commas. "Newton, the great mathematician, was very modest." "And he, their prince, shall rank among my peers." In such sentences, however, as, "The mathematician Newton was very modest," and "The Emperor Napoleon was a great soldier," commas are not used.
The name or designation of a person addressed is isolated by commas. "It touches you, my lord, as well as me." "John, come here." "Mr. President, my object is peace." "Tell me, boy, where do you live?" "Yes, sir, I will do as you say." "Mr. Brown, what is your number?"
Pairs of words.--"Old and young, rich and poor, wise and foolish, were involved." "Sink or swim, live or die, survive or perish, I give my hand and heart to this vote." "Interest and ambition, honor and shame, friendship and enmity, gratitude and revenge, are the prime movers in public transactions."