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I get stuck by the following sentence from this article: Noam Chomsky: The False Promise of ChatGPT.

The crux of machine learning is description and prediction; it does not posit any causal mechanisms or physical laws.

I thought crux is an uncountable noun, but it turns out that its plural is cruces. Therefore, I am wondering why not the form of 'cruces' + 'are': The cruces of machine learning are description and prediction;

If the New York Times article is right, then I thought this umbrella form should also be right: singular noun + is + something + and + something

For instance, these sentences:

  1. My key to happiness is mindfulness and forgiving.
  2. The crime enabler is Tom and John.

I don't think they are right at all.

One of my attempts to solve this myself:
The aforementioned 'crux' sentence should be comprehended as 'The crux of machine learning is (the combination/integration of) description and prediction'

What am I missing? Thanks in advance.

Lerner Zhang
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    Quoting the entire sentence: The crux of machine learning is description and prediction; it does not posit any causal mechanisms or physical laws. This puts crux in context, but requires a more nuanced explanation of Chomsky's article to fully understand. –  Sep 16 '23 at 01:22

1 Answers1

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You presumably prefer the subject ("the crux of machine learning") to be in plural form because the predicate nominative ("description and prediction") is apparently in plural form. However, there is no requirement that the numbers agree. Usually they agree for the sake of logic, but sometimes they don't. Here is an example:

A tonic is both a kind of drink and a concept in music theory.

For more discussion and examples, see Araucaria's answer here, Joachim's answer here, and MZS's answer here.

In addition, "description and prediction" is plural in form but not necessarily in construction. We often treat such phrases as singular when the two conjuncts are closely related. (This is usually discussed in the context of subjects; for example, see tchrist's answer to this question.)

  1. My key to happiness is mindfulness and forgiving.
  2. The crime enabler is Tom and John.

I don't think they are right at all.

I'd consider the first sentence to be possibly acceptable, but the second doesn't seem to work because there seem to be multiple enablers. However, something like this is often considered acceptable:

Out of all of the two-man bobsledding teams, the best one is Tom and John.

MarcInManhattan
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  • For the three related question links, I think the question of this helpful answer differs from mine, and this question relates also to the ambiguous plurality as the first one, and the last one is the most related, but the difference lies in the object. In that case, the object is the plural of a noun. – Lerner Zhang Sep 16 '23 at 06:41
  • I am wondering if there is a grammatical rule for such patterns or not? – Lerner Zhang Sep 16 '23 at 06:43
  • @LernerZhang If by "grammatical" you mean based only on syntax, word classes, etc. (ignoring semantics), then no, there is no general rule. If one thing can be considered equivalent somehow to multiple things, then it's fine to say "[sing. subject] is [plural pred. nom.]". And if the pred. nom. is plural in form but singular in construction, then it's fine to say "[sing. subject] is [pred. nom. that is sing. in construction]". Some subjectivity is involved, and some sentences will sound fine to some people but awkward to others. – MarcInManhattan Sep 16 '23 at 16:51