Punctuation that changes meaning

A missing comma rarely stops a reader, but it does stop a proofreading test. Employers who test proofreading are hiring for documents where a comma changes the amount, the date or the party responsible, so the tests are strict about them.

Commas

• After an introductory phrase: "After the meeting, send the notes."
• Around a non-essential clause: "The invoice, which was sent on Monday, is overdue."
• Between items in a list. Whether the final comma before "and" is used depends on the house style; be consistent.
• Not between a subject and its verb: "The manager who approved it, has left" is wrong.

Apostrophes

Possession: the client's file (one client), the clients' files (many). Contraction: it's = it is; its = belonging to it. Plurals never take an apostrophe: "the 1990s", "three PDFs".

Hyphens

Use a hyphen when two words act as one adjective before a noun: a long-term plan, a 60-second test. Leave it out after the noun: the plan is long term. "Re-sign" and "resign" are different words.

Full stops in abbreviations and numbers

Match the document's own style. If it uses "Mr" without a stop in one place, it should everywhere. Decimal points and thousands separators follow the region: 1,250.00 in India and Nigeria, 1.250,00 in much of Europe.

In a test, punctuation errors are usually fewer than wrong-word errors but worth the same marks. Scan for them on your second pass, when you are reading sentence by sentence.