Et al., Ibid., Op. Cit.: Citation Abbreviations Explained

Et al. means "and others" and replaces the names of additional authors. APA 7 uses it from three authors on; MLA 9 does too. Ibid. means "in the same place" and appears mainly in Chicago notes, though Chicago now prefers short notes. Op. cit. and loc. cit. are old forms that modern styles rarely want.

What do these citation abbreviations mean?

Each abbreviation is a Latin phrase that saves repeating details in a citation. Here is the short version before the rules.

The two you will meet most are et al. and ibid. If you are writing for a course, the style guide your instructor names always overrides general advice, including this page.

Et al. meaning and how to use it

Et al. shortens a list of authors so a citation stays readable. Two details trip up writers: the punctuation and the number of authors that triggers it.

Punctuation and italics

• Write et al. with a period after "al." only. "Et" is a complete word and takes no period.
• Do not italicize it in APA, MLA or Chicago. Older guides sometimes italicized Latin terms, but the current editions treat et al. as an ordinary English phrase.
• No comma goes before et al. in APA or MLA. APA adds a comma after it, before the year: (Okafor et al., 2021). MLA has no comma at all: (Okafor et al. 214).
• Do not use it for two authors. Two authors are always both named.

Et al. in APA 7

APA 7 (the seventh edition, 2019) uses et al. in the text from the first citation when a work has three or more authors.

• One author: (Okafor, 2021)
• Two authors: (Okafor & Reyes, 2021)
• Three or more authors: (Okafor et al., 2021)

In a sentence, write "Okafor et al. (2021) found..." In the reference list, APA 7 lists the names of up to 20 authors. If a work has 21 or more, list the first 19, then an ellipsis, then the final author. Et al. is not used in the reference list entry itself.

One exception: if two different works would shorten to the same form, for example Okafor, Reyes, and Lin (2021) and Okafor, Wang, and Tran (2021), add as many author names as needed to tell them apart, then et al.

Et al. in MLA 9

MLA's ninth edition uses et al. for three or more authors, both in the text and in the works cited list.

• Two authors: (Okafor and Reyes 214)
• Three or more: (Okafor et al. 214)
• Works cited: Okafor, Ngozi, et al. Title of Book. Publisher, 2021.

Notice that MLA writes "and", not "&", and puts no comma between author and page number.

Et al. in Chicago

Chicago's two systems differ. In author-date, cite up to three authors by name and use et al. from four authors on. In notes and bibliography, a note names up to three authors and shortens a four-or-more author work to the first name plus et al. The bibliography lists up to ten authors; for more than ten, list the first seven followed by et al. Edition details change, so check the edition your institution uses.

Et al. in Harvard and other styles

Harvard is not one fixed style, so the number varies by university. Many versions use et al. from three or more authors, some from four. Always check your department's Harvard guide. IEEE and some science styles use et al. in the text from three authors, and some medical styles show only the first few names followed by et al. in the reference list.

Ibid. meaning and how to use it

Ibid. tells the reader that a citation is the same as the one immediately before it. It belongs to footnote and endnote systems, where citations sit in numbered notes.

In Chicago notes, it looks like this:

1. Maria Santos, The Harbour Towns (Lisbon: Atlantic Press, 2018), 42.
2. Ibid., 57.
3. Ibid.

Note 2 is the same book, a different page. Note 3 is the same book and the same page as note 2. In note 3, "Ibid." stands alone with a period.

Three things to remember:

• It points only to the immediately preceding note. If another source comes between, you cannot use it.
• Capitalize it at the start of a note, and follow it with a comma and the page if the page changes.
• Do not italicize it. Since its 17th edition (2017), Chicago has advised avoiding ibid. in favor of shortened notes, giving the author's last name, a short title and the page, for example: Santos, Harbour Towns, 57. Ibid. is still accepted, but short notes are safer because they stay clear if you rearrange your text.

APA and MLA do not use ibid. at all. In APA you repeat the author-date citation each time. In MLA you repeat the author and page, or only the page if the author is named in your sentence.

Op. cit. and loc. cit.: why they are rarely used now

Op. cit. points back to a work already cited, with only the author's name and a new page: Santos, op. cit., 88. Loc. cit. points to the same passage. Both force a reader to hunt backwards through earlier notes to find the full details, especially in long documents. Because shortened notes solve the same problem more clearly, current Chicago guidance and most university guides discourage them. You may still see them in older books and some humanities journals, and a few departments still allow them, so follow your own style sheet.

Quick reference by style

Worked examples

APA in-text, four authors. Source: Okafor, N., Reyes, L., Lin, T., and Haddad, S. (2021).

• Wrong: (Okafor, Reyes, Lin, & Haddad, 2021)
• Right: (Okafor et al., 2021)

MLA works cited, three authors.

• Wrong: Okafor, Ngozi, Luis Reyes, and Tina Lin. Writing Across Fields. Hartwell, 2021.
• Right: Okafor, Ngozi, et al. Writing Across Fields. Hartwell, 2021.

Chicago notes, same book twice in a row.

1. Santos, Harbour Towns, 42.
2. Santos, Harbour Towns, 57.

This short form needs no ibid. and is easy to follow.

Common mistakes

• Writing "et al" without the final period.
• Writing "et. al." with a period after "et".
• Using et al. for two authors.
• Using ibid. when another source sits between two notes.
• Italicizing et al. or ibid. in APA, MLA or Chicago.
• Mixing styles, for example MLA-style et al. rules inside an APA paper.
• Assuming your reference list uses et al. the same way as the in-text citation. The rules for the list differ in every style.

Checklist

1. Which style and edition does the assignment require?
2. Count the authors. Is it two, three or more?
3. Does that style trigger et al. at that number, in the text and in the list?
4. If you use notes, is ibid. permitted, or should you use short notes?
5. Are the periods and italics right?
6. Does the reference list match the text?

Use AdeptWrite for the tedious parts

The Citation Generator builds references in APA 7, MLA 9, Chicago, Harvard and IEEE from the details you enter, in your browser. It uses English abbreviations such as et al., pp. and n.d. Generated entries should always be checked against your style guide, because editions and local variants differ. Run your finished draft through the Grammar Checker to catch stray punctuation, and see Latin abbreviations for e.g., i.e. and other terms. For the full style rules, read the APA 7 citation guide, the MLA format guide and in-text citations.

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