Stops, brackets, dashes and spacing
Punctuation marks show where a sentence ends, how its parts relate and how an aside interrupts the main thought. Full stops, semicolons, colons, question marks, parentheses and dashes serve different purposes; their placement also affects emphasis and ease of reading.
Full stops, semicolons and questions
Commas, semicolons, periods and question marks are stops that help sentence cadence and clarity. A period, or full stop, ends a sentence; periods also appear in abbreviations such as Mr., Ph.D. and Dr..
A comma should not take the place of a full stop between the two sentences in the leaflet example “Bendroflumethiazide tablets can cause dizziness, make sure you are not affected before driving or operating machinery”. The suggested revision separates the warning and instruction: “Bendroflumethiazide can cause dizziness. If you feel dizzy, do not drive or operate machinery.”
A semicolon can join closely related thoughts where a full stop would separate them too sharply; the choice can be a matter of individual style. It can also separate items in a series when commas are needed within those items. An illustrative list separates rest; analgesics or muscle relaxant medication; and physical therapy including heat, ice, and stretching exercises.
A direct question ends with a question mark: “The physician asked the patient, ‘Where is the pain located?’” An indirect question ends with a period: “The physician asked the patient where the pain was located.”
Colons
A colon should not interrupt a transitive verb and its direct object, a participle and its object, or a preposition and its object. The disruptive forms include measures included: the Fugl-Meyer assessment, several measurements including: the irregularity index and such as: approaches. A complete sentence should precede a colon introducing a list.
A colon can distinguish a general category from the examples that follow it. In a sentence describing T-cell accumulation in CCL25 expression sites, a comma before the intestinal epithelium and the intestinal lamina propria can make sites look like the first of three items. Replacing that comma with a colon identifies the following two locations as the expression sites.
Parentheses, paired commas and paired dashes
Parentheses, paired commas and paired dashes can interrupt a sentence to introduce a related comment. Their uses overlap, and a practical approach is to choose according to the comment's strength and degree of digression.
Paired commas mark transitional or parenthetic expressions closely related to the surrounding thought. Parentheses signal material subordinate and nonessential to the main text, such as an aside or interjection. Paired dashes can mark an abrupt change of thought, an added point or explanatory comment, often with emphasis or dramatic effect.
One suggested three-way distinction gives each mark a different degree of departure from the main sentence.
- Paired commas enclose straightforward explanatory material closely integrated with the sentence: “Urinary tract infection, so common in females, is difficult to treat.”
- Parentheses enclose more digressive but related material: “Urinary tract infection (E. coli or Klebsiella) is difficult to treat.” The same example could also take commas or paired dashes.
- Paired dashes enclose the strongest interjection, a definite departure that adds meaning or emphasis: “Urinary tract infection—how devastating!—is difficult to treat.” Strong emphasis, startling opinion or comic relief can take this form.
Another emphasis hierarchy places the em dash first for emphasis, the comma next for slight emphasis, and parentheses last for de-emphasis.
Punctuation load and tone
A finished text should be checked for excessive punctuation, especially repeated brackets or commas that can irritate readers. Just give (an) example(s) can be recast with such as to remove the distracting brackets.
An exclamatory tone is rarely appropriate in a scientific argument, but an exclamation mark can highlight a hazard or strengthen a prohibition. An illustrative cyanide warning uses it to emphasise that avoiding ingestion or inhalation alone is insufficient: “It is not enough just to avoid drinking the solution or inhaling the gas!”
Em-dash spacing
Both spaced and unspaced em dashes are used in US publishing. A style account quoted in 2009 described most newspapers and many popular magazines as using spaces, while most books and journals omitted them.
Three typographic versions of one phrase allow direct comparison.
- “…give the dash—also commonly known as the em dash—some breathing space…”
- “…give the dash — also commonly known as the em dash — some breathing space…”
- “…give the dash— also commonly known as the em dash— some breathing space…”
An informal survey reported in 2009 included ten people: three did not care either way but preferred preserving the status quo, three strongly preferred spaces before and after the dash, and four had no strong feelings but thought spaces perhaps made more sense. Six had not previously given the issue much thought, and none knew why the unspaced dash had become preferred in books and journals. The sample was informally selected and probably biased.
The argument for adding spaces concerns the reader's visual and mental movement through a digression; leading and trailing spaces do not change the dash's literary function or the digression's meaning.