Consider the following imperative-sentence structure

Do 𝑋 and do π‘Œ.

(Source: https://www.chicagomanualofstyle.org/qanda/data/faq/topics/Commas/faq0067.html ) where I believe (but do not know this for sure) that the two β€œdo”s are two placeholders for two occurrences of one or two verbs.

Example from mathematics:

Note that π‘š < 𝐿 and apply (*).

Here, (*) is the reference to another formula.

This sentence can be viewed as two independent clauses connected by a conjunction or as a single clause with a compound predicate, cannot it? Why?

Another example in the same vein:

Note that 𝐿 β©½ [ … a long chain of inequalities occupying slightly more than one line … ] < (πΊβˆ’1)𝐿 and apply (*).

How about this one? Do we have a compound predicate or two independent clauses? Why?

For each of the two exemplary sentences: is a comma before β€œand”

  1. necessary,

  2. forbidden,

  3. optional with a change in the meaning, or

  4. optional without a change in the meaning?

PS. Note that we do not refer to poetry or even high-level prose here (where the writers sometimes take their liberty to intentionally abuse the language to make a point) but rather to daily usage in business, technical documentation, sciences, newspapers and journals (naturally, first class and no yellow press).

  • BTW, while "can't it" is grammatical, "cannot it" is not; it has be "can it not". Commented Dec 8, 2021 at 21:44
  • @Acccumulation If you know this for sure, please go on and edit. Thanks in advance!
    – user142975
    Commented Dec 8, 2021 at 21:45
  • A compound predicate means multiple verbs apply to the same subject. So "Do X and do Y". is not an example of a compound predicate. John washed and dried the car. is an example of a compound predicate.
    – Lambie
    Commented Dec 8, 2021 at 22:15
  • 1
    @Acccumulation To split red herrings, I'm not sure I would say that "cannot it" is not grammatical, but it's not idiomatic (at least, not at the end of a sentence, and not lately Commented Dec 8, 2021 at 22:30
  • 1
    As I punned, it's both a distraction from your main question and an academic quibble. I wouldn't advise using "cannot it" in everyday modern speech. This has a lot to do with trends around inversion when negating. Shakespeare has Oberon ask "Am not I thy lord?" but Richard II ask "Am I not king?" I'm not sure, but I wonder whether usage was already trending toward the later in his time, and he was making Oberon loftily archaic... Commented Dec 8, 2021 at 22:46

2 Answers 2


The point you seem to miss is whether you analyse this as "two clauses with a coordinator" or "two clauses in a compound predicate". The meaning is exactly the same. There are two things you are commanded to do.

The point of compound predicates is that you can rephrase

John went to the shops and John ate a sandwich.


John went to the shops and ate a sandwich.

with no change in meaning

So in the imperative you can rephrase

Go to the shops and eat a sandwich.


Go to the shops and eat a sandwich.

with no change in meaning.

But in the imperative there is no change in form and no change in meaning. So it totally doesn't matter.

Commas are optional, with no change in meaning.

  • Concerning "two clauses in a compound predicate": I thought that a compound predicate consists of verbs, not of clauses, doesn't it?
    – user142975
    Commented Dec 8, 2021 at 21:40
  • As for the commas, they are IMHO forbidden in case of a compound predicate and necessary in case of two long independent clauses, aren't they? So, it's NOT the case that β€œit totally doesn't matter”, is it?
    – user142975
    Commented Dec 8, 2021 at 21:42
  • Well, I the point being missed (pardon the passive) is that: "Do 𝑋 and do π‘Œ." is not: "Note that π‘š < 𝐿 and apply (*)." The first repeats the verb do, and the second has two different verbs: note and do. [You wrote "Go to the shops and eat a sandwich" twice, the same way. Did you mean to do that?]
    – Lambie
    Commented Dec 8, 2021 at 21:43
  • I don't use examples with "do". Yes the point is that there is no way of distinguishing the grammatical structure nor the meaning. The words are the same, the meaning is the same. Only the arbitary grammatical label is different. So just don't bother with the label.
    – James K
    Commented Dec 8, 2021 at 21:48
  • We know what "Go to the shops and eat a sandwich." means. Who cares whether it is called "compound predicate" or "coordinated clauses"
    – James K
    Commented Dec 8, 2021 at 21:49

Yes, each of your example sentences can be interpreted either as one clause (containing one subject and two predicates) or as two clauses (each containing one subject and one predicate). I'll demonstrate with your first sentence:

[[You]] do 𝑋 and do π‘Œ.
[[You]] do 𝑋 and [[you]] do π‘Œ.

(The same can be done with your other sentences, even if the two verbs are different.)

In general, a comma must be included whenever a FANBOYS conjunction connects two main clauses, but the comma is often omitted with short clauses. How short? There is no fixed rule, and this issue has been discussed on SE, for example here: https://english.stackexchange.com/questions/119839/when-to-use-a-comma-before-and. It's therefore impossible to state definitively which of your four options is correct, but let me give some examples:

Necessary: "Girls proceed directly to the left by the gymnasium, and boys walk to the right by the cafeteria." (However, some people might consider a comma optional even in this case.)
Forbidden: "Oh, well. Live and learn." (I don't think that any reasonable person would insert a comma before "and".)
Optional with a change in the meaning: "Walk and feed the dog." vs. "Walk, and feed the dog."
Optional without a change in the meaning: "Walk around the block and feed the dog." vs. "Walk around the block, and feed the dog."

  • I think it is a big mistake to say forbidden. No one is forbidding anything. Also, a writer might want to use: Live, and learn. To signal a pause.
    – Lambie
    Commented Dec 8, 2021 at 22:09
  • @Lamblia β€œLive, and learn” sound as if you have to live first and learn second. Good luck with learning after having lived.
    – user142975
    Commented Dec 8, 2021 at 22:30
  • 1
    @Lambie Fair enough. Perhaps considering something "forbidden" should be forbidden. Commented Dec 9, 2021 at 0:54

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