Punctuation. Commas

    The content of these guidelines is taken from the third edition of the Vives University Network’s Interuniversity Style Guide for Writing Institutional Texts, an interuniversity project in which the UPC participates with the support of the Secretariat for Universities and Research of the Government of Catalonia.


      General guidelines

      • As a general rule, commas can be used to list items in a series, to join sentences and to set off parenthetical or introductory phrases.
      • For commas in lists in sentence form, see Items in lists.


      Listing items in a series

      • In a list containing a series of items, separate the items with commas. However, a comma should not precede the conjunction before the final item (in other words, write a, b and c and not a, b, and c). But if a comma would make the meaning clearer, use it – especially where one of the items in the list is already joined by and.

        Specialist subjects include teaching, research and development, and business applications.


      Joining sentences

      • When you join two complete sentences into a single sentence, you can use commas but follow them with a suitable connecting word: and, or, but, while or yet.

        The group members had to hand in their reports last week, but some were only submitted this week.

      • The comma is not required if the subject of the second part of the sentence is omitted or if the conjunction used is and or or.

        The student had to hand in the work by Friday but didn't make the deadline.
        The student had to hand in the work by Friday or the work would receive a failing mark.


      Other uses of commas

      • Separate a city from a state, province, region or country with a comma.

        Chicago, Illinois Lisbon, Portugal

      • Do not use a comma between the month and the year.

        October, 2001 October 2001

      • In most numbers of one thousand or more, use commas between groups of three digits, counting from the right.

        62,242 1,723 1,000,000

      • Exceptions are degree temperatures, years, addresses, page numbers and other uses of numbers for a non-quantifying purpose (see Numbers and commas).


      Misuse of the comma

      • Do not put a comma between the subject and the verb even if the subject is very long. Therefore, in the sentence below there is no comma between the words own (the end of the long subject) and are (the first word of the verb phrase).

        Students who are attracted by the idea of spending a few months studying at a university in a country other than their own are often put off when they realise they will have to attend lectures in a foreign language.