Is "et al." used as a singular or plural subject?

Solution 1:

The Latin translates into Gamma and others, so the verb should be plural if the subject is construed as the authors. However, if the subject is construed to be the article, a singular entity written by three or more authors, e.g., the Gamma et al. article, then the sentence can be written as Gamma et al. says that... -- this is, however, rare, in my experience, and, like walkmanyi, I would avoid it if possible.

When I edit biomed articles, I always treat this structure as a plural subject and ensure plural subject-verb concord: Gamma et al. (2009) say that....

Solution 2:

We can take different approaches to answering this.

Trying to analyse it, I have to conclude that since et al means "and others" that I would treat it as plural just as I would if I'd simply used the English "Gamma and others are saying" rather than "Gamma and others is saying".

We can look at patterns of usage. Here this look at google ngrams suggests the use of the singular. However, it's close and neither are very common. This look at ngrams uses more possible verbs, and finds that generally the plural is more heavily used, and much more with "...et al have" vs "...et al has".

So far it would seem that we should definitely use the plural. A counter-argument is that we often use the author or authors of a text to refer to the text itself. If this is the case, then it should be treated as plural. However, that doesn't seem to be the usage here, and indeed we could say that this may explain some of the singular use found by examining ngrams above, so in fact it actually adds weight to the argument in favour of plural use. It does suggest that the following are both correct though:

"Gamma et al are saying..." referring to the authors.

"[Gamma et al] is saying..." referring to the text, where the bibliography has an entry of that and for some reason we prefer not to just list it as "[Gamma]".

Solution 3:

First of all, my answer won't be authoritative regarding English grammar, I base it on observed patterns in literature.

Is it correct to grammatically treat this as one person or multiple persons?

As you stated your examples, it would be clearly plural, since you are speaking about a group of authors, even though mixed with Latin. That is "Gamma et al. are saying in their text..."

Having said that, there are multiple uses of "Name et al.". Besides speaking about a group of authors, this can also refer to a particular work, such as a book, or a paper mentioned earlier. An example would be the second sentence of the following: an algorithm has a complexity X (Name et al.). That is, Name et al. bases the analysis on Y and continues with .... However, personally, I would try to avoid such constructions altogether - if possible.

Solution 4:

The Ngram is not helpful in this situation. The following sentence works: An Experimental Approach to the Development of Insect Wings by Smith, W, et al. is a useful resource; however, "Smith, W. et al. suggest that my daughter should not have been born with wings" ain't that bad either. Ask yourself, "What is the subject of the sentence, the work itself or the authors of the work?"