If only there were a single rule! The number of noun-noun combinations in English is virtually infinite, and there are no rules for their formation. There are classes of combinations, and we can look at some of them, starting with the examples in the question.

"Cow's milk" is the correct form. It is not a compound noun; it belongs to the class of noun-noun combinations known as the descriptive genitive*, or classifying genitive**. This kind of combination consists of the genitive (possessive) form of a noun plus a second noun. The relationship between the two nouns can be possessive, as in calves' liver and bird's nest, or it can be a for-relationship, as in women's college and children's games. Sometimes the first noun is singular, and sometimes it is plural.

"Car battery" is the correct form (unless one is referring to the battery of a particular car). This combination belongs to a different kind of noun-noun combination, some of which are called noun compounds, or compound nouns (as in bar code or lamp post), and others of which are just noun + noun sequences (e.g. pilot project or sushi bar). There is no clear dividing line between these two kinds of combinations, and each combination must be learned individually. The descriptive genitive is treated in Quirk et al., Section 5.122.* A helpful discussion of all types of noun-noun combination can be found in Biber et al., Sections 4.8.2 and 8.3.**

Marilyn Martin
*Quirk et al., A Comprehensive Grannar of the English Language, Longman, 1985
**Biber et al., Longman Grammar pf Spoken and Written English,
Marilyn's posting states just how difficult it is to make a rule to govern the formulation of noun + noun combinations.

Students at beginning levels and above ask this very question: how can we know when to use a possessive as in "cow's milk" or a noun adjective as in "cow milk"?

One of the first things we can tell our students is that *often* -- ("often" is a key word here)-- the apostrophe + S structure is used to talk about parts of people's and animals' bodies.

"a man's leg"
"an elephant's trunk"
"a sheep's heart"

But to talk about parts of non-living things, we usually use the noun + noun structure or the of structure.

"a table leg" (NOT a table's leg)
"the car door" (NOT the car's door)
"the roof of a house" (NOT "the house's roof")

The expression "cow's milk" does not exactly fit the category of part of a living thing. These expressions might be "cow's legs", "a cow's brain," or "cows' hooves." There is another category described in Swan to refer to something produced by or from living animals; this would include "cow's milk" as well as "lamb's wool," "sheep's wool,"bird's egg," and "hen's egg." Irregularities appear here, too, though, as in expressions such as "camel hair" and "horsehair."

Another subdivision is noted: when the animal is killed to provide something, we usually use the noun + noun combination, as in "calf skin," "fox fur," "chicken soup," and "lamb chop," in contrast to the apostrophe + S combination for living beings as in "cow's milk."

So this topic of classifying expressions to modify nouns is indeed complicated, and certainly too complicated to analyze for students. The first step in clarifying this for students, though, might be to contrast living things from inanimate things, as in the classic "table leg" or "leg of the table" vs. "the child's leg."


*Practical English Usage, Second Edition, by Michael Swan. Oxford University Press. 1995

[This message was edited by Grammar Exchange on April 05, 2003 at 10:20 PM.]

[This message was edited by Grammar Exchange on April 06, 2003 at 08:54 AM.]
What happens if I want to say: the capicity of computers.
Is it grammaticaly correct to say "computers capacity"? or should I say computer capacity? since "computer" functions as an adjective and adjectives do not have plural forms. But if th correct way is computer capacity How would a reader know that I am not talking about one computer but several?

Thanks in advanced
Hello, Stephanie, and welcome to the Grammar Exchange.

We would say either 'computer capacity' or 'the capacity of the computer(s).

'Computer capacity' is a classic example of nouns that become adjectives and don't have -S at the end, even if the word refers to a noun in the plural. This is the original rule. Thus, we have the following, as examples, all of which have a singular noun/adjective form, and we are not sure whether the noun consists of one item or more than one:

  • apple tree
  • egg salad
  • shoe store
  • dog house
  • banana milkshake

    So, even if the first noun is in its singular form, it may refer to more than one item. In your sentence, you could say:

  • You need more computer capacity that you have.

  • The capacity of this computer/ these computers is very small.
  • Hello, Saman:

    It is possible to use either 'information system department' or 'information systems department.' Google shows about 57,000 examples of 'information system department,' and 155,000 examples of 'information systems department.'

    From those figures, and from my own observations, however, I believe that 'systems' would be the more usual adjective. Noun adjuncts that refer to communications are very often formed with the noun itself in the plural. Thus we have communications specialist, systems analyst, systems operator, etc.

    In addition, take a look at this definition of 'ISD.' It shows 'Information SystemS Division' and Information SystemS Development':


    Because this grammar point -- noun modifiers being in the singular or plural form -- has many items unfixed in our vocabulary, you might be able to use either the singular 'system' or the plural 'systems' in this case. However, with the word 'system,' it seems that we are almost set on the plural form as the adjective.
    Hello, Suk, and welcome to the Grammar Exchange!

    It's nice to see that you have found this old thread that was started almost 14 years ago, and that you now come to us with a related question. That shows how well our forum works, and how more useful it becomes every year.

    English is a complicated -- but fascinating -- language, and there are many different mechanisms for word and phrase formation. Marilyn and Rachel explained some of them very nicely in the past.

    If INFORMATION SYSTEMS DEPARTMENT is correct, then 4 YEARS OLD BOY is wrong and must be 4-year-old boy?

    In "information system(s) department," you have a series of nouns, in which "information" modifies "system(s"), and "information system(s)" modifies "department." Instead, the adjective "four-year-old" is formed by a numeral, a noun in the singular, and an adjective. This word-formation mechanism is perfect for measures:

    - a lane that is ten meters long is a ten-meter-long lane.
    - a lake that is twenty meters deep is a twenty-meter-deep lake.
    - a shirt that costs ten dollars is a ten-dollar shirt (in this case, no adjective is used)

    Notice that the plural after the numeral disappears. Isn't it extraordinary?


    That is, I think, because in that way "New Year" remains as a unit, and "new" does not refer to "resolutions" but to "year." In this particular case, however, I think it's only more idiomatic to say "New Year's resolutions" than "New Year resolutions." If "new" referred to "resolutions," we'd probably change the noun "year" to the adjective "yearly" or "annual."
    we should say "in our school's policy" or "in our school policy"?

    Remember that direct questions in English require inversion, so your question above should have been:

    - Should we say "in our school's policy" or "in our school policy"?

    And, similarly, your questions further above should have been:

    - Then is 4 YEARS OLD BOY wrong?

    - Why is it not NEW YEAR RESOLUTION?

    In answer to your latest question, my answer is that both forms are correct. This is related to this explanation of Rachel's:

    "Car battery" is the correct form (unless one is referring to the battery of a particular car).

    In "our school's policy," emphasis is made on the policy of this specific school. Instead, in "our school policy," "school" is merely a noun in attributive position that defines what sort of policy we are speaking about: it is not a company policy, or a government policy -- it is a school policy.

    Note: Next time you ask a question, it'd be better if you provided more context, that is, full sentences or paragraphs containing the words or phrases your ask us about.
    our school uniform. not our school's uniform.

    Hi, Terry,

    Although "school uniform" is much more common that "school's uniform," the second form can be used, especially if a specific school is mentioned or its name is provided, as is the case here: https://books.google.com.ar/bo...q=%22bolton%20school's%20uniform%22&f=false .

    "school uniform" is more usual because the noun "school" typically characterizes "uniform." Instead, in "school's uniform," an owner-possession relationship is established, as can be seen in the example I quoted, and that is not so common.

    Hi, back again to this old thread (:

    >>so what about (Brain cell regeneration)<<

    1- Is cell singular or plural?

    2- Is it possible if we mean one cell in (Brain cell regeneration)

    3-Why we cannot useS plural in cell :like>{ Brain cells regeneration}


    Hello, Bande, and welcome to the Grammar Exchange!

    I'll take the liberty to transcribe part of a paper I once wrote based on an old thread from this forum, in turn based on Quirk.

    Should count nouns premodifying other nouns, that is to say, placed in attributive position before other nouns, be used in the singular or in the plural?

    Traditionally, we have learned to use the singular form for noun modifiers (as is the case with “drug dealer” rather than “drugs dealer,” which also exists but is much less frequent than the former, or “shoe factory” instead of “shoes factory”), except in the following cases described by Quirk:


    When the premodifying plural noun is highly institutionalized and its singular form might lead to ambiguity:


    an Arts degree (a degree in the humanities) as opposed to: an art degree (a degree in fine art)

    a services agreement (an agreement to render/receive services) as opposed to: a service agreement (an agreement to provide a single service, such as maintenance)


    When there is no singular form of a noun (these nouns, such as “goods,” “clothes,” “scissors,” are known as pluralia tantum)


    a customs officer


    When there is a need to denote variety or plurality of members (Quirk says: “There is a tendency for more generic terms to be plural and more specific terms to be singular.”)


    a sports magazine (“sport” is generic, so we can think of many possible sports) [but] a football magazine

    a shareholders meeting (companies have more than one shareholder)


    When a topical issue comes forth, often in newspaper stories:


    the Wikileaks scandal

    However, Quirk says that “the plural attributive construction is on the increase…”

    In answer to your specific question, Bande, although both "brain cell regeneration" and "brain cells regeneration" can be used, the former is much more usual for the reasons specified above.


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