et al. rules: how many authors before you shorten

Two different questions

Almost every et al. mistake comes from treating this as one rule. It is two. The first is how many authors you name in an in-text citation before shortening. The second is how many you list in the reference list entry. The numbers are different in every style, and usually the list threshold is much higher.

The reasoning is straightforward once stated. The in-text citation exists to point at an entry in your list, so it needs to be short and unambiguous. The list entry exists to record the work, so it names as many contributors as is practical.

So a paper by six authors is (Nakamura et al., 2024) in text and all six names in the reference list, if you are writing APA. Shortening the list entry to one name and et al. loses information a reader may need and is one of the fastest things for a marker to spot.

The thresholds, side by side

APA 7 is the one that changed. In APA 6, three-to-five-author works were cited in full on first mention and shortened afterwards. APA 7 removed that: three or more authors take et al. from the very first citation. A great many guides online still describe the old rule.

Punctuation, in one line

It is 'et al.' — two words, no italics, a full stop after 'al' and none after 'et'. The abbreviation is of et alii, and 'al.' is the shortened word, which is why only it takes the stop.

Italics were standard decades ago and are not now, in any of the major styles. If your reference manager is italicising it, that is a template setting rather than a rule.

The full stop stays even mid-sentence: "(Nakamura et al., 2024) found...". At the end of a sentence, do not double the stop.

Two works that shorten to the same citation

This is the situation the thresholds are designed around, and every style has a rule for it. If Nakamura, Ali and Brown (2024) and Nakamura, Ali and Costa (2024) both shorten to (Nakamura et al., 2024), a reader cannot tell them apart.

APA's solution: name as many authors as it takes to distinguish them, then et al. — so (Nakamura, Ali, & Brown, 2024) and (Nakamura, Ali, & Costa, 2024). This applies from the first citation and to every subsequent one.

MLA and Chicago take the same approach in substance. Harvard practice varies, with some institutions preferring a letter suffix on the year instead. Check your handbook, and whichever you use, be consistent.

This is worth checking in any literature review that draws on a productive research group, because that is exactly where the same lead author publishes repeatedly with overlapping teams.

The verb after et al.

Et al. stands for several people, so the verb is plural: "Nakamura et al. argue", not "argues". This trips people up because the visible subject is a singular name.

The same holds for a two-author citation joined by 'and'. Only a single author or a corporate author takes a singular verb — and corporate authors are a genuine grey area, where British usage often prefers the plural ("the government have") and academic writing generally prefers the singular.

Pick one convention for corporate authors and hold it through the document. Inconsistency there is more noticeable than either choice.

Ampersands, 'and', and where each belongs

APA uses an ampersand inside parentheses and the word 'and' in running text: (Nakamura & Ali, 2024) but "Nakamura and Ali (2024) found". Harvard variants generally use 'and' in both positions, though a few institutions follow the APA split.

MLA uses 'and' everywhere. Chicago uses 'and' in notes and bibliography.

This is a small thing that markers notice because it is easy to check and appears dozens of times in a document. A search for ' & ' in your finished draft takes ten seconds and catches every instance.

What et al. does to your reference manager

The thresholds above are template settings, and every reference manager ships with defaults that may not match your institution's Harvard variant — of which there are many, differing on exactly this point.

Before you write forty citations, produce one test document with a two-author, a three-author, a six-author and a twenty-author paper, and compare the output against your handbook. Fixing the template once is far cheaper than fixing the output afterwards.

If your institution publishes its own style file for Zotero or EndNote, use it. That is what it exists for, and it settles every question on this page in advance.

Author counts in the sciences

Some fields routinely publish papers with dozens or hundreds of authors, and the reference list rules were written with those in mind. APA's twenty-author rule, with its ellipsis before the final name, exists because listing four hundred names is not useful to anyone.

Where a paper is authored by a consortium — a collaboration name rather than individuals — cite the consortium as a corporate author. This is now the norm in genomics, particle physics and large clinical trials, and it is what the papers themselves do.

Check how the paper asks to be cited. Many large collaborations state the preferred citation form on the article's first page, and following it is both correct and easier.

Repeat citations, ibid and short forms

Once et al. has done its work, the next question is what to do when you cite the same source three sentences later. APA, Harvard and MLA answer it the same way: repeat the citation in full each time, because a reader may enter your text anywhere.

The footnote styles differ. Chicago and OSCOLA allow a shortened form after the first full citation — author surname, a short title, and the pinpoint — and both allow ibid for an immediately preceding source, though OSCOLA has moved away from the older Latin abbreviations op cit and loc cit entirely.

Never use ibid across a page break in a printed document without checking, and never use it in a document whose footnote numbering might change. It is the citation form most likely to end up pointing at the wrong source after an edit.

Where you cite one source repeatedly through a long passage, most styles allow a single citation at the end of the passage covering it, provided the text makes clear the whole passage draws on that source. Say so explicitly rather than relying on the reader to infer it.

One habit that prevents most errors

Write the reference list entry first, in full, and derive the in-text citation from it. Doing it the other way round — writing (Nakamura et al., 2024) as you draft and reconstructing the entry later — is how authors go missing.

It also makes the two-question structure obvious in practice, because you can see the full author string in front of you when you decide how much of it the in-text citation needs.