Comma, Semicolon, Colon - Punctuation

AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Comma, Semicolon, Colon

Commas, semicolons, and colons can be used to indicate a break or pause in thought, to set off material, or to introduce a new but connected thought. Each of these punctuation marks has specific uses, and the strength of the break in thought determines which mark is appropriate.

8.2.1 Comma.

Commas are the least forceful of the 3 marks. Although comma usage sometimes is subjective, there are definite rules for using commas. Follow these rules unless overriding considerations (such as clarity) require otherwise. Separating Groups of Words.

The comma is used to separate phrases, clauses, and groups of words and to clarify the grammatical structure and the intended meaning.

Use a comma after opening dependent clauses (whether restrictive or not) and long opening adverbial phrases.

If the infection recurs within 2 weeks, an additional course of antibiotics should be given.

When you have to pay for your own health care, does your consumption really become more efficient?

A comma is optional if the introductory phrase is short.

In some patients midazolam produces paradoxic agitation.

Use commas to set off nonrestrictive subordinate clauses (see 7.2.2, Relative Pronouns) or nonrestrictive participial phrases.

Ms Frederick, who had been waiting on hold for more than an hour, abandoned all hope of having her questions answered.

The numbness, which had been apparent for 3 days, disappeared after drug therapy.

The delegates, attaining consensus, passed the resolution.

But avoid setting off a phrase with commas where doing so would make the meaning ambiguous.

Avoid: Although numerous investigators have called for measures to improve sight in nursing home residents, to our knowledge, none have attempted a study of the effect of a vision restoration-rehabilitation program on function and quality in this population.

In the example above, it is not clear whether the phrase “to our knowledge” applies to what precedes it or what follows it. Removing the comma after “to our knowledge” makes the meaning clear.

Better: Although numerous investigators have called for measures to improve sight in nursing home residents, to our knowledge none have attempted a study of the effect of a vision restoration-rehabilitation program on function and quality in this population.

Use a comma to avoid ambiguous or awkward juxtaposition of words.

Outside, the ambulance siren shrieked.

Still, noting the trends and highlighting the lack of funding for achieving world health goals do not translate into more positive actions.

Use commas to set off appositives. Commas precede and follow the apposition.

Two colleagues, John Smith and Amari Bhatnager, worked with me on this study.

The battered child syndrome, a clinical condition in young children who have experienced serious physical abuse, is a frequent cause of permanent injury or even death. Series.

In a simple coordinate series of 3 or more terms, separate the elements by commas (see 7.1.1, Nouns as Modifiers).

Each patient was asked to complete a 21-item, 7-point, self-administered online questionnaire.

Use a comma before the conjunction that precedes the last term in a series to prevent ambiguity; this is often referred to as a serial comma or Oxford comma.

Outcomes result from a complex interaction of medical care and genetic, environmental, and behavioral factors.

The physician, the nurse, and the family could not convince the patient to take his medication daily.

While in the hospital, these patients required neuroleptics, maximal observation, and seclusion.

However, a series of 3 or more modifiers should not be separated by commas when the modifiers are seen as 1 term or entity:

The patient has chronic progressive multiple sclerosis.

Gray matter magnetic resonance imaging was used to determine longitudinal brain atrophy.

Judgment and common sense are required in interpreting this rule. If the order of the adjectives can be rearranged without loss of meaning or clarity, use the comma.

A physician’s personal response to the patient and the patient’s illness seems to violate the ideal of an objective, standardized, replicable view of the case.

Practicing medicine is a unique, intricate, rewarding lattice of learning and relearning.

Note: When fewer than 3 modifiers are used, avoid adding a comma if the modifiers and the noun are read as one entity:

We conducted a randomized placebo-controlled trial.

Data from multicenter administrative databases were analyzed. Names of Organizations.

When an enumeration occurs in the name of a company or organization, the comma is usually omitted before the ampersand or and. However, follow the punctuation used by the individual company or organization, except in references (see 3.12.8, References to Books, Publishers).

Farrar, Straus and Giroux

Little, Brown and Company


Zeig, Tucker & Theisen

Houghton Mifflin Harcourt Setting Off ie and eg.

Use commas to set off ie and eg and the expanded equivalents, that is and for example.

The use of standardized scores, eg, z scores, has no effect on statistical comparisons.

The most important tests, that is, the white blood cell and platelet counts, were unduly delayed.

Note: If an independent clause follows these terms or their equivalents, precede the clause with a semicolon.

Our double-blind study compared continuous with cyclic estrogen treatment; ie, estrogens for 4 weeks were compared with estrogens for 3 weeks followed by placebo for 1 week.

It may also be set off with parentheses.

Our double-blind study compared continuous with cyclic estrogen treatment (ie, estrogens for 4 weeks were compared with estrogens for 3 weeks followed by placebo for 1 week). Separating Clauses Joined by Conjunctions.

Use commas to separate independent clauses joined by coordinating conjunctions (and, but, or, nor, for, yet, so).

Plasma lipid and lipoprotein concentrations were unchanged after low-intensity training, but high-intensity training resulted in a reduction in triglyceride levels.

No subgroup of responders could be identified, and differences between centers were so great that no real comparison was possible.

If both clauses are short, the comma can be omitted.

The test may be useful or it may be harmful.

I have read the article and I am concerned about the data collection methods.

Unless the comma is needed for readability, do not insert a comma before the coordinating conjunction in a compound predicate.

These facilities are beginning to resemble “minihospitals” and are losing their identity as freestanding ambulatory surgery centers.

Clauses introduced by yet or so and subordinating conjunctions (eg, while, where, after, whereas) are preceded by a comma (see 11.1, Correct and Preferred Usage of Common Words and Phrases).

He taught medical students, performed careful research, and wrote thoughtful articles, yet was denied tenure.

The United States spends more than $1000 per capita per year on paperwork related to health care, whereas Canada spends only approximately $300 per capita.

One recent study found that low literacy was associated with worse mental health, whereas another concluded that literacy was not associated with depression.

If yet or so appear at the beginning of a sentence, they should not be followed by a comma.

I have seen many cases of vertigo. Yet this one was particularly troubling. Setting Off Parenthetical Expressions.

Use commas to set off parenthetical words, phrases, questions, and other expressions that interrupt the continuity of a sentence (eg, therefore, moreover, on the other hand, of course, nevertheless, after all, consequently, however) (see 8.8.1, Punctuation, Ellipses, Omission Within a Sentence).

The real issue, after all, was how to fund the next study.

Therefore, we were disappointed that the article did not include consideration of medical schools and their influence on the culture of medicine.

What is needed, then, is collective empowerment of practitioners, guided by accountability to the public.

Note: In some cases, removal of the commas around parenthetical expressions changes the meaning of the sentence. In the example immediately above, then suggests a summing-up. Without these commas, then suggests time, ie, what comes next. Setting Off Degrees and Titles.

Academic degrees and titles are set off by commas when they follow the name of a person. Although it is not incorrect to set off Jr and Sr by commas when they follow the name of a person, the JAMA Network journals do not use these commas.

Berton Smith Jr, MD, and Priscilla Armstrong, MD, PhD, interpreted the radiographic findings in this study.

Joyce Fredrickson-Smith, MD, PhD, vice-chancellor, attended the conference on health care reform. Addresses.

In running text and affiliation footnotes, use commas to separate the elements in an address. Use commas after the city and state or country name. (Note: In US and Canadian addresses, commas are not used before the zip or postal code.)

This year, the editorial board meeting will be held in conjunction with the annual meeting at the Westin Bonaventure Hotel and Suites, 404 S Figueroa St, Los Angeles, CA 90071.

Dr Majeed may be reached at the Department of Primary Care and Public Health, Imperial College London, Reynolds Bldg, London W6 8RP, England.

The study was conducted at The Wilmer Institute, Baltimore, Maryland, in 2010. Dates.

In dates and similar expressions of time, use commas according to the following examples. Commas are not used when the month and year are given without the day or between a holiday and its year.

The first issue of JAMA was published on Saturday, July 14, 1883.

The patient’s rhinoplasty was scheduled for August 19, 2014, at Strong Memorial Hospital, with postoperative evaluation on August 30.

The terrorist bombings in Boston, Massachusetts, in April 2013 led to further examination of preparedness for major disasters.

The publication offices were closed on New Year’s Day 2013. Numbers.

In accordance with SI convention, separate digits with a thin space, not a comma, to indicate place values beyond thousands (see 17.4.3, Use of Numerals With Units, Number Spacing).


12 345

615 478

9 473 209

As of September 2013, the Centers for Disease Control and Prevention estimated that 1 148 200 persons 13 years and older are living with HIV infection, and almost 1 in 5 (18.1%) are unaware of their infection.

A comma may be used to separate adjacent unrelated numerals if neither can be expressed easily in words, but it is preferable to reword the sentence or spell out one of the numbers.

By December 2003, 929 985 cases of AIDS had been reported in the United States.


By December 2003, a total of 929 985 cases of AIDS had been reported in the United States.

See 3.6, References, Citations, and 4.1.6, Tables, Punctuation. Units of Measure.

Do not use a comma between 2 or more measures whose units are the same dimension (eg, time or volume).

3 years 4 months 2 days old

3 lb 4 oz

gestational age of 32 weeks 6 days or 32 6/7 weeks Placement.

The comma is placed inside quotation marks (see 8.6.5, Punctuation, Quotation Marks, Placement) and before superscript citation of references and footnote symbols.

As a result of the “back-to-sleep campaigns,” a call has been issued for a “back-to-the-bench” campaign.

These missed opportunities occur during office visits,6-9 health department appointments,10-13 and hospitalizations.16 To Indicate Omission.

The comma is used to indicate omission or avoid repeating a word when the sense is clear (see 7.5.7, Shift in Number of Subject and Resultant Subject-Verb Disagreement).

Four patients could not be studied: in 1, duration of treatment was too short; in 3, too long.

A plus indicates present; a minus, absent.

Commas are also used in titles of news items to replace and when space is limited.

Malaria Vaccine, Ebola Therapy Promising in Early Studies Dialogue.

Commas are often used before direct dialogue or conversation is introduced (see, Punctuation, Comma, Semicolon, Colon, Colon, Introducing Quotations and Enumerations).

In the middle of the laboratory examination, a student asked, “Would it be OK to take a break?”

8.2.2 Semicolon.

Semicolons represent a more definite break in thought than commas. Generally, semicolons are used to separate 2 independent clauses. Often a comma will suffice if sentences are short, but when the main clauses are long and joined by coordinating conjunctions or conjunctive adverbs, especially if 1 of the clauses has internal punctuation, use a semicolon. Separating Independent Clauses.

Use a semicolon to separate independent clauses in a compound sentence when no connective word is used. In most instances it is equally correct to use a period and create 2 sentences.

The conditions of 52% of the patients improved greatly; 4% of the patients withdrew from the study.

However, if clauses are short and similar in form, use a comma.

Seventy grafts were patent, 5 were occluded.

Use a semicolon between main clauses joined by a conjunctive adverb (eg, also, besides, furthermore, hence, however, indeed, then, thus, yet) or a coordinating conjunction (and, but, for, nor, or, yet, so) if one of the clauses has internal punctuation or is long.

The patient’s fever had subsided; however, his condition was still critical.

The word normal is often used loosely; indeed, it is not easily defined.

Introduction to the knowledge, skills, and attitudes relevant to safety should begin in medical and nursing school; eg, the first 2 years of medical school may be the most appropriate to learn error science and principles of leadership. Enumerations.

For clarity, use semicolons between items in a complex or lengthy enumeration within a sentence or in an enumeration that contains serial commas in at least 1 of the items listed. (In a simple series with little or no internal punctuation, even with multiword elements, use commas.) (See 18.5, Enumerations.)

A number of questions remain unresolved: (1) whether beverages that contain caffeine are an important factor in arrhythmogenesis; (2) whether such beverages can trigger arrhythmias de novo; and (3) whether their arrhythmogenic tendency is enhanced by the presence and extent of myocardial impairment.

Research questions examined the group’s (1) origin, development, and operation; (2) influence; and (3) implications for modern practice.

The photomicrographic illustrations of the gross and microscopic features of normal skin, Spitz congenital and dysplastic nevi, lentigines, and melanoma demonstrated the complexity of pigmented lesions.

In less formal writing and where the last element of a series is also a series, commas are acceptable provided that clarity is preserved.

The statistician addressed limitations in case-control studies, cohort studies, and randomized, double-blind, controlled trials.

8.2.3 Colon.

The colon is the strongest of the 3 marks used to indicate a decided pause or break in thought. It separates 2 main clauses in which the second clause amplifies or explains the first.

This dictum is often believed to be in the Hippocratic Oath: First, do no harm.

See also last example in, Introducing Quotations or Enumerations. When Not to Use a Colon.

Do not use a colon if the sentence is continuous without it.

You will need enthusiasm, organization, and a commitment to your beliefs.


You will need: enthusiasm, organization, and a commitment to your beliefs.

Avoid using a colon to separate a preposition from its object or to separate a verb (including to be in any of its manifestations) from its object or predicate nominative.


The point is: do not insert the catheter at this time.


The point is to not insert the catheter at this time.

Do not use a colon immediately after because or forms of the verb include.


Symptoms of asthma include: wheezing, trouble breathing, chest tightness, and cough.


Symptoms of asthma include the following: wheezing, trouble breathing, chest tightness, and cough.

Still better:

Symptoms of asthma include wheezing, trouble breathing, chest tightness, and cough.

Do not use a colon between a title and subtitle when the title concludes with other punctuation (see, Question Mark, Placement, and, Exclamation Point, Placement). Introducing Quotations or Enumerations.

Use a colon to introduce a formal or extended quotation. (If the sentence to follow is in quotation marks, the first word is capitalized.)

Harold Johnson, MD, chair of the committee, summarized: “The problems we face in developing a new vaccine are numerous, but foremost is isolating the antigen.”

Use a colon to introduce an enumeration, especially after anticipatory phrasing such as thus, as follows, the following.

The solution included the following components: phosphate buffer, double-distilled water, and a chelating agent.

Laboratory studies yielded the following values: hemoglobin, 11.9 g/dL; erythrocyte sedimentation rate, 104 mm/h; calcium, 16.9 mg/dL; phosphorus, 5.6 mg/dL; and creatinine, 3 mg/dL.

Phytoestrogens are subdivided into 3 main classes: isoflavones, lignans, and cumestrans.

If 2 or more grammatically independent statements follow the colon, they may be treated as complete sentences separated by periods, and the initial words may or may not be capitalized.

The following procedure has been established for updating the journal’s Instructions for Authors: (1) Update and review the Word file. (2) Style the Word document according to guidelines and send to the electronic media staff. (3) Insert links. (4) Proofread final version. (5) Code and post on the web. Numbers.

Use a colon to separate chapter and verse numbers in biblical references, hours and minutes in expressions of time, and the elements of ratios when they are expressed as numbers or abbreviations. For ratios expressed as words, use the word to rather than a colon unless the term conventionally takes a hyphen (eg, “cost-benefit ratio”). In that case, follow the conventional usage and use a hyphen.

The first mention of leprosy in the Old Testament is found in Exodus 4:6.

Medication was given twice a day, at 8:30 AM and 8:30 PM.

The chemicals were mixed in a 4:3 ratio.

The study participants and controls were randomized in a 2:1 ratio.

The ACTH:TSH ratio was elevated when the patient was first examined.

The ratio of albumin to globulin was one of the outcome measures in the study.

The student to instructor ratio was 7:1. References.

In references, use a colon (1) between title and subtitle (unless the title ends with a question mark or an exclamation point); (2) for periodicals, between issue number and page numbers; and (3) after “doi” (see 3.0, References).