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Is this sentence grammatically correct?

All butterfly is colourful.

In my opinion I think it should be,

All butterflies are colourful.

but according to Grammarly the sentence is correct.

Can someone explain please. Thank you.

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    I think we should do the walls half butterfly, half ladybug. No, it should be all butterfly because it’d be more colorful. All butterfly is colorful, but she loves ladybugs as well and will cry if there aren’t any. – Jim Jul 6 '18 at 5:05
  • All butterflies are colorful. Grammarly are sometimes stupid. – Hot Licks Jul 6 '18 at 20:07
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You are correct—and Grammarly is wrong.

While it's theoretically possible for the set of "all butterflies in the room," for example, to consist of a single member (just one butterfly), there are three problems with this.

First, there is typically no immediate way of knowing if there is just a single butterfly.

Second, the sentence in question does not include a qualifier like "in the room" in the first place. Without that, it means "every butterfly in existence." It's not true that only one butterfly exists.

Finally, regardless of the possibility of the count of all resolving to a single item, grammar usage is that all is associated with a plural noun—assuming that the noun is countable. (We could, for instance, write all water.)

This is similar to the fact that every and each are followed by a singular noun.

So, regardless of the rest of the sentence, all butterfly is, on its own, ungrammatical.

We need to say all butterflies. Given that, we also need to say are colourful.

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Not everything that is grammatical from a strictly analytical perspective is either meaningful or idiomatic.

Consider

All wealth is fleeting.

All spaceflight is costly.

All paper is fibrous.

All lamb is high in protein.

All butterfly is colorful.

The first four examples all sound natural. Wealth and spaceflight are concepts, paper and lamb are substances, and so all refers to all such things in existence, and non-count nouns are treated as singular. We are not talking about individual rocket launches or individual baby sheep.

It is theoretically possible to use butterfly in this manner, and grammatically, strictly speaking, this would be permitted. But no one would ever refer to butterfly as a substance (or abstract concept) normally. One would do intentionally for literary effect, such as the jocular utility of its atypicality, along the lines of I don't wanna get Daewoo on my hands


So-called grammar checkers do not, for the most part, actually check grammar. As with machine translations, what most of them do is compare text against millions of similarly phrased texts that they have been "trained" on. If it looks like something known to be wrong, it is flagged. My guess is that Grammarly would correctly identify All butterflies is or All butterfly are as ungrammatical. You just found an edge case of an unusual phrasing which is correct in a very narrow technical sense and wrong in every practical sense.

  • "The steed bit its master. / How came this to pass? / It heard the good pastor / Say, 'All flesh is grass.'" – tautophile Jul 6 '18 at 22:21
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You're right. Grammarly isn't right all of the time, and this is one of those times. I can only imagine that Grammarly is somehow picking up "butterfly" as something other than a count noun, maybe as a noncount noun. I can't really be sure.

What I am sure of is that "all butterflies" is a third-person, plural subject, so the ensuing verb "be" must be conjugated into the third-person, plural, present-tense conjugation "are."

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  • Only Grammarly knows its grammar rules. Even if they published them, we don't know its software in order to see if it is processing them properly. Most automated grammar checkers will have some idiosyncrasies, some false positives, some false negatives. It is best to use grammar checkers not to fix all your grammar, but as a check for obvious mistakes.

  • Whether either of those is grammatical, depends a lot on context. To be sure, the first one all by itself sounds horrible and is 'incorrect' in all known varieties of English (that I can imagine). But there may well be some strange convoluted context in which 'all butterfly' is treated as a singular.

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But no, the intended meaning is not "All butterflies are colorful," so the syntax is different and it works. Grammarly is not in error.

While choster has taken note of one possibility (though notes at the same time that it may not quite work for "butterfly" because it's a bit different from the other examples), here is the other perspective.

The intended meaning could as well be:
"There is no part of a butterfly that not colorful." So that, "All (of a) butterfly is colorful."

This works with all nouns in all contexts.

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