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Correct the sentence:

The ebb and flow of the tides / are / now understood.

In the above sentence I can go by two ways:

  1. First is that according to are I should be using the before flow thus making ebb and flow as the two different entities.
  2. Second is that since it is given as The ebb and flow , I can consider it as a single entity and use is in place of are.

Or is it that since tides is given , I need to go with are. I'm quite confused. Suggestions please.

  • 1
    I think @CopperKettle has covered everything in his answer, but this page from Purdue University has some rules for compound subjects that I've found helpful owl.english.purdue.edu/owl/resource/599/01 – ColleenV Oct 3 '15 at 15:52
  • "is" can be correct depending on what you mean, but "are" sounds more natural because "tides" is plural. It might be better to write "the tide" instead of "the tides" and avoid the issue. Better still, you can avoid the passive voice entirely as long as you have a subject in mind: "we now understand the ebb and flow of the tides." – shadowtalker Oct 3 '15 at 15:52
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The ebb and flow of the tides / are / now understood.

I'll introduce some jargon. The ebb and flow is a compound subject that uses the coordinating conjunction and. Compound subjects joined by and are usually treated as plural and consequently need a plural verb:

John and Sarah are moving to Moscow this summer.

However, if the compound subject represents a single idea or a person, it is treated as a unit and a singular verb is used with it:

Ham and eggs is a popular breakfast dish.

"The ebb and flow (of something)" can clearly be treated as a single unit:

The ebb and flow of Iranian political fortunes has created opportunities and challenges for the development of Omani political and commercial interests in... (Google Books, "Oman, Culture and Diplomacy ", Jeremy Jones, ‎Nicholas Peter Ridout - 2012)

And the same phrase has been sometimes treated as a combination of units in literature:

"This is particularly true when the ebb and flow of relationships between specific areas have to be examined." ("The First Western Greeks", David Ridgway, 1992)

"Though fashion's impact is not restricted to dress, the ebb and flow of clothing styles have historically been the most controversial of all the practices in virtually every cultural community." (Beverly Lemire, 2010)

"Up and down the historical route which leads from Baghdad to the heart of Persia the ebb and flow of battle were very marked in 1916." (Sir Percy Sykes, "A History of Persia")

However, these quotes, or some of them, could serve as examples of deviation from the predominant perception of "ebb and flow" as a single unit, or even slight errors. Wait for native speakers' opinions.


My guess is that it's up to the author. If they want to stress the wholeness of the subject, they might use a singular verb, or they might use a plural in order to stress the distinctness of "ebb" and "flow".

  • 1
    Very well explained. Thanks. But, if I am given only this sentence and find the error in it. How would I go with that because I don't have the situation then. – Seema Bhukar Oct 3 '15 at 8:40
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    @SeemaBhukar - I guess you can safely cross out are and put is in its stead. Training materials often overlook nuances of meaning, their main purpose is to teach the basics of a language. – CowperKettle Oct 3 '15 at 8:42
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    @SeemaBhukar - quoting a native English speaker and an ardent grammarian Snailboat's reaction to my "Persia" quote above, "Oh, interesting! My ear expects was.". Which means you can safely use is. (0: – CowperKettle Oct 3 '15 at 8:52
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    @Seema Moreover, you can safely put it as "The ebb-and-flow (process) of the tides" with no change in meaning, which removes all doubt. – Buckminster Oct 3 '15 at 9:30
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    @Seema Well, it is strange. Which book is it? E.g., consider the explanation here: psckerala.net/index.php/psctopic/sub/… ("You can use 'ebb and flow' to describe the way that something repeatedly increases and decreases or rises and falls: ebb and flow (singular)." Besides, there's no such idiom as 'the ebb and the flow', it's only 'the ebb and flow'. The information you provided sounds pretty unusual. – Buckminster Oct 3 '15 at 15:29
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Since the question has drawn some attention and nevertheless stays unclear, here's an extract on the topic (taken from Errors in English Composition by J. C. Nesfield, 1903):

Two singular subjects followed by a singular verb

Three different cases arise:

  1. When the two singular nouns refer to the same person or thing, and have but one article or other qualifying word in front of them, the verb is singular. In such a case the plurality is apparent, not real.

    • The poet and statesman is dead.

    This is equivalent to saying, “The man who was both poet and statesmen is dead.” If different persons had been intended, the sentence would have been, “The poet and the statesmen are dead.” Note, that here the article is repeated.

  2. When the two singular nouns are practically synonymous, one being added to the other for the sake of emphasis or elucidation, the verb may be singular. No plurality is felt to exist in such a case.

    • Wherein doth sit the fear and dread of kings. – Shakespeare.
    • The peace and good order of society was not promoted by the feudal system.
    • The very scheme and plan of his life differed from that of other men.
  3. When the two singular nouns, though not synonymous, are intended to express jointly a single idea or a single whole, the verb may be singular:

    • Bread and butter is what they usually have for breakfast.
    • The ebb and flow of the tides is now understood.
    • The style of a man should be the image of his mind, but the choice and command of language is the fruit of experience.

Though the examples above are all more than a century old, I presume the grammar behind them remains valid. Also note in which case the article is repeated: when the two singular nouns refer to different things.

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