A sentence in a book I am reading says “ Behind every system of actions are a system of beliefs”. Why is it “are” instead of “is”?

This is not correct. The verb "are" is supposed to be applied to "a system" (when every is used, assume singular), so the correct way to write this would be "behind every system of actions is a system of beliefs". This is an easy mistake to make because people will mistakenly try to match the plurality of the verb to "actions".

I see two possibilities. The first is an error, where the author mistakenly wrote "are" to accord with "actions", rather than "system". The second possibility is that the book is British in origin, which sometimes pluralizes collective nouns that would be singular in North American English (you'll hear British sports commentators say things like "Manchester *are* undefeated...", while North Americans would say "Manchester *is* undefeated". Given the context, I would lean toward the former as I don't think rules about collective nouns would apply here.

If you said "a set of beliefs" then "are" is the correct word, but I would use "is" for "a system of beliefs".

Regional difference, this is correct in some versions of English. Yes, 'a system' is singular, but it \*represents\* multiple things. In some areas you would say, "My company is planning to do X" because company is singular. But in some places you say, "My company are planning to do X" because there are multiple people involved in the company and the verb 'to be' is conjugated with that understanding.

The problem the writer is struggling with is that the ‘correct’ form: “Behind every system of actions is a system of beliefs” Suggests that there might only be one system of beliefs that lies behind all the different systems of actions.  So the writer’s instinct is to go for a plural verb to emphasize that there are multiple systems of belief, that this ‘a’ can’t be interpreted as ‘one’. But having reached for that plural they have failed to land it with a plural noun because that would make it sound like there might be more than one system of beliefs behind every system of actions: “Behind every system of actions are systems of beliefs” What they’re trying to do is communicate a one-to-one correspondence.  And I think weirdly, they’ve managed to - which makes me question whether this is actually ‘wrong’.  But they could probably have gone with “Behind every system of actions is some system of beliefs” “Behind every system of actions is a corresponding system of beliefs” “Behind all systems of actions are corresponding systems of beliefs” Or maybe you could get there with “Behind all systems of actions are systems of beliefs”

The sentence feels clunky to me too. I'd say it's just a genuine grammatical error in the print.

It should be "is". You can remove prepositional phrases to determine this. Behind every system (of actions) is a system (of beliefs). Behind every system is a system. The book made a typo.

This is a common error. The subject is ‘system’, a singular noun. The writer misidentified ‘actions’ as the subject, but that’s really the object of the prepositional phrase ‘of actions’ which is modifying the subject. Since the subject is singular, the verb also must be singular.

I'm going out on a limb here. Generally the verb will agree with the subject, right? But some subjects are connected to another one and therefore they're the whole of it, like a system of something is the whole total amount of it. So I believe it says "are", because it's a "system of beliefs", the writer felt like expressing themselves that way, it did work, so it's fine. Correct me if I'm wrong, please.

It’s an error, caused by the proximity of a plural form to the verb.

You’re correct. That’s an error. Behind every system of this is a system of that.

It's an error, most likely caused by incorrectly thinking *action* is the subject of the verb of being. It should be "system . . . is."

Presumably, the use of *are* is because of *action****s*** (a plural). Technically, this is wrong, because a system is a collective singular

Sometimes book editors miss things.

It's wrong, but even native speakers can fail to properly match nouns and verbs when the sentence is complex. It's more common in speech, where you might start your sentence one way, and then change it as you are saying it, and now things don't match. An editor should have caught that.

>Behind every system of \[X\] is a system of \[Y\]. Behind all systems of \[X\] are systems of \[Y\]. You're right that it should be 'is' instead of 'are' because the word 'system' is singular.

Are you reading Atomic Habits by chance?

I would use is.

They are wrong, you are right. 

Because they are dumb. 🤪

Collective singular nouns like "system" used to be treated as plural. For example "the crowd are getting restless" and "the crowd is getting restless" are both correct sentences. The wording you've read is a little archaic, but valid.

I literally just watched my wife make the same mistake while translating a sentence into English from Japanese in Duo. We're native English speakers.

It's a mistake. Because the verb are is conjugated for system and not actions it should be conjugated as 'is' because system is singular. Occasionally when the verb comes after a word that is plural even though it is an action being performed by a singular noun you will see someone use the plural conjugation of the verb by accident. It's not uncommon to see one or two errors to slip past the editors of a book, but hopefully the book isn't full of errors.

You’re correct. The verb “are” is applied to “a system of beliefs” and not “every system of actions”. It makes more sense when you read it like this: Behind every system of actions, are a system of beliefs. This is a mistake that made it through editing.