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Cheryl Iverson

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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.

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.

Not: 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 all of its manifestations) from its object or predicate nominative.


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


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

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

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, 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.


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 Old Testament mention of leprosy is in Exodus 4:6.

Medication was given twice a day, at 8:30 am and at 8:30 pm.

The chemicals were mixed in a 4:3 ratio.

The study subjects 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 to 1.


In references, use a colon (1) between title and subtitle; (2) for periodicals, between issue number and page numbers; and (3) for books, between publisher’s location and name. (See also 3.0, References.)

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