Rulebase

Commas with Parenthetical Expressions

The Comma

Rulebase Summary

Use commas to set off parenthetical expressions — words, phrases, or clauses that interrupt the smooth flow of the sentence or that come at the end. Common examples include 'I believe,' 'if any,' 'in effect,' 'in fact,' 'as a matter of fact,' 'if I remember correctly,' 'to tell you the truth,' 'from the moment I met him,' etc. When a parenthetical expression precedes the conjunction in a compound sentence, keep the comma before the conjunction and add one after the parenthetical expression.

Morson's Rule 73 · p.45 BGGP Separating Comma.34 · p.200 BGGP Separating Comma.43 · p.207 BGGP Setting-Off Comma.17 · p.227 BGGP Setting-Off Comma.18 · p.227 BGGP Parenthetical.1 · p.362 BGGP Though.5 · p.407 BGGP However.2 · p.409

Examples

✗

A. The payment I believe was due on the first of the month.

✓

A. The payment, I believe, was due on the first of the month.

Parenthetical 'I believe' set off with commas.

✗

A. The results as a matter of fact were exactly what we predicted.

✓

A. The results, as a matter of fact, were exactly what we predicted.

Parenthetical expression interrupts — commas around it.

⚠

Style Guides Disagree

When a long adverb clause or long prepositional phrase interrupts a 'that' clause — landing between the introductory 'that' and the words that complete it — authorities agree a comma is needed after the interrupting element, where the sentence rejoins the 'that' clause. They differ on whether a matching comma belongs in front of it. One approach reads the interrupter as parenthetical and sets it off on both sides (the leading comma stays); another reads it as essential or introductory to the embedded clause and uses only the closing comma (the leading comma is dropped). Both are accepted, so the leading comma is a reporter-preference call rather than a fixed rule. Note that this is a paired-comma construction, not a single comma standing between a verb and its object.

Transcript Notes

Two tests identify a parenthetical: (1) it can be moved around within the sentence without changing the meaning or structure, and (2) it can be dropped into any sentence and the sentence will make sense.

If the parenthetical is in the middle of the sentence, it is surrounded with commas. Expressions like 'I believe,' 'it seems to me,' and 'I'd say' are parenthetical when they appear mid-sentence and are surrounded with commas.

When these same expressions begin the sentence, they are the main subject and verb and do not take punctuation.

Style Guide References (8)

Morson's

Rule 73 Page 45

BGGP

Separating Comma.34 Page 200

BGGP

Separating Comma.43 Page 207

BGGP

Setting-Off Comma.17 Page 227

BGGP

Setting-Off Comma.18 Page 227

BGGP

Parenthetical.1 Page 362

BGGP

Though.5 Page 407

BGGP

However.2 Page 409
See also (16)
Related Comma with Filler Words (You Know, I Mean, Like, Okay, See) Compare Semicolon Before Conjunctive Adverbs and Transitional Expressions Compare Dashes Around a Complete Thought Dropped Inside a Sentence Compare Comma (or No Comma) After Conjunctive Adverbs Based on Syllable Count and Context Related Comma with a Nominative Absolute Related Comma with a Nonessential Participial Phrase Related Comma with 'Who,' 'Which,' 'Whom,' and 'In Which' Clauses Related Comma with 'Together With,' 'As Well As,' 'Accompanied By,' etc. See Introductory Element Comma Rules Apply Regardless of a Leading Coordinate Conjunction Compare Comma After a Long Introductory Prepositional Phrase Compare Comma After an Objective Case Noun Clause Pulled to the Beginning of a Sentence Related Comma with Nouns of Direct Address Related Periods and Lowercase for i.e. and e.g. Same topic Comma with 'Please,' 'Too,' and 'Also' Compare No Comma Between Subject and Verb, Verb and Object, or Verbal and Completer Compare No Comma Before an Essential Adverbial Clause