For other uses see Noun (disambiguation).
Lexical categories are defined in terms of how their members combine with other kinds of expressions. The syntactic rules for nouns differ from language to language. In English, nouns may be defined as those words which can occur with articles and attributive adjectives and can function as the head of a noun phrase.
The word comes from the Latin nomen meaning "name". Word classes like nouns were first described by the Sanskrit grammarian and ancient Greeks like Dionysios Thrax; and were defined in terms of their morphological properties. For example, in Ancient Greek, nouns inflect for grammatical case, such as dative or accusative.
Expressions of natural language have properties at different levels. They have formal properties, like what kinds of morphological prefixes or suffixes they take and what kinds of other expressions they combine with; but they also have semantic properties, i.e. properties pertaining to their meaning. The definition of a noun at the outset of this page is thus a formal, traditional grammatical definition. That definition, for the most part, is considered uncontroversial and furnishes the propensity for certain language users to effectively distinguish most nouns from non-nouns. However, it has the disadvantage that it does not apply to nouns in all languages. For example in Russian, there are no definite articles, so one cannot define nouns as words that are modified by definite articles. There are also several attempts of defining nouns in terms of their semantic properties. Many of these are controversial, but some are discussed below.
In traditional school grammars, one often encounters the definition of nouns that they are all and only those expressions that refer to a person, place, thing, event, substance, quality, or idea, etc. This is a semantic definition. It has been criticized by contemporary linguists as being uninformative. Contemporary linguists generally agree that one cannot successfully define nouns (or other grammatical categories) in terms of what sort of object in the world they refer to or signify. Part of the conundrum is that the definition makes use of relatively general nouns ("thing", "phenomenon", "event") to define what nouns are. The existence of such general nouns demonstrates that nouns refer to entities that are organized in taxonomic hierarchies. But other kinds of expressions are also organized into such structured taxonomic relationships. For example the verbs "stroll","saunter", "stride", and "tread" are more specific words than the more general "walk". Moreover, "walk" is more specific than the verb "move", which, in turn, is less general than "change". But it is unlikely that such taxonomic relationships can be used to define nouns and verbs. We cannot define verbs as those words that refer to "changes" or "states", for example, because the nouns change and state probably refer to such things, but, of course, aren't verbs. Similarly, nouns like "invasion", "meeting", or "collapse" refer to things that are "done" or "happen". In fact, an influential theory has it that verbs like "kill" or "die" refer to events,  which is among the sort of thing that nouns are supposed to refer to. The point being made here is not that this view of verbs is wrong, but rather that this property of verbs is a poor basis for a definition of this category, just like the property of having wheels is a poor basis for a definition of cars (some things that have wheels, such as my suitcase or a jumbo jet, aren't cars). Similarly, adjectives like "yellow" or "difficult" might be thought to refer to qualities, and adverbs like "outside" or "upstairs" seem to refer to places, which are also among the sorts of things nouns can refer to. But verbs, adjectives and adverbs are not nouns, and nouns aren't verbs, adjectives or adverbs. One might argue that "definitions" of this sort really rely on speakers' prior intuitive knowledge of what nouns, verbs and adjectives are, and, so don't really add anything over and this. Speakers' intuitive knowledge of such things might plausibly be based on formal criteria, such as the traditional grammatical definition of English nouns aforementioned.
Another semantic definition of nouns is that they are prototypically referential. That definition is also not very helpful in distinguishing actual nouns from verbs. But it may still correctly identify a core property of nounhood. For example, we will tend to use nouns like "fool" and "car" when we wish to refer to fools and cars, respectively. The notion that this is prototypical reflects the fact that such nouns can be used, even though nothing with the corresponding property is referred to:
John is no fool.
If I had a car, I'd go to Marrakech. The first sentence above doesn't refer to any fools, nor does the second one refer to any particular car.
The British logician Peter Thomas Geach proposed a very subtle semantic definition of nouns. He noticed that adjectives like "same" can modify nouns, but no other kinds of parts of speech, like verbs or adjectives. Not only that, but there also doesn't seem to be any other expressions with similar meaning that can modify verbs and adjectives. Consider the following examples.
Good: John and Bill participated in the same fight.
Bad: *John and Bill samely fought.There is no English adverb "samely". In some other languages, like Czech, however there are adverbs corresponding to "samely". Hence, in Czech, the translation of the last sentence would be fine; however, it would mean that John and Bill fought in the same way: not that they participated in the same fight. Geach proposed that we could explain this, if nouns denote logical predicates with identity criteria. An identity criterion would allow us to conclude, for example, that "person x at time 1 is the same person as person y at time 2". Different nouns can have different identity criteria. A well known example of this is due to Gupta:
Proper nouns (also called proper names) are nouns representing unique entities (such as London, or Johnny), as distinguished from common nouns which describe a class of entities (such as city, planet or person). Proper nouns are not normally preceded by an article or other limiting modifier (such as "any" or "some"), and are used to denote a particular person, place, or thing without regard to any descriptive meaning the word or phrase may have.
In English and most other languages that use the Latin alphabet, proper nouns are usually capitalized. Languages differ in whether most elements of multiword proper nouns are capitalised (e.g., American English House of Representatives) or only the initial element (e.g., Slovenian Državni zbor 'National Assembly'). In German, nouns of all types are capitalized. The convention of capitalizing all nouns was previously used in English, but ended circa 1800. In America, the shift in capitalization is recorded in several noteworthy documents. The end (but not the beginning) of the Declaration of Independence (1776) and all of the Constitution (1787) show nearly all nouns capitalized, the Bill of Rights (1789) capitalizes a few common nouns but not most of them, and the Thirteenth Constitutional Amendment (1865) only capitalizes proper nouns.
Sometimes the same word can function as both a common noun and a proper noun, where one such entity is special. For example the common noun god denotes all deities, while the proper noun God references the monotheistic God specifically.
Owing to the essentially arbitrary nature of orthographic classification and the existence of variant authorities and adopted house styles, questionable capitalization of words is not uncommon, even in respected newspapers and magazines. Most publishers, however, properly require consistency, at least within the same document, in applying their specified standard.
The common meaning of the word or words constituting a proper noun may be unrelated to the object to which the proper noun refers. For example, someone might be named "Tiger Smith" despite being neither a tiger nor a smith. For this reason, proper nouns are usually not translated between languages, although they may be transliterated. For example, the German surname Knödel becomes Knodel or Knoedel in English (not the literal Dumpling). However, the transcription of place names and the names of monarchs, popes, and non-contemporary authors is common and sometimes universal. For instance, the Portuguese word Lisboa becomes Lisbon in English; the English London becomes Londres in French; and the Greek Aristotelēs becomes Aristotle in English.
See main article: Count noun and Mass noun. Count nouns are common nouns that can take a plural, can combine with numerals or quantifiers (e.g. "one", "two", "several", "every", "most"), and can take an indefinite article ("a" or "an"). Examples of count nouns are "chair", "nose", and "occasion".
Mass nouns (or non-count nouns) differ from count nouns in precisely that respect: they can't take plural or combine with number words or quantifiers. Examples from English include "laughter", "cutlery", "helium", and "furniture". For example, it is not possible to refer to "a furniture" or "three furnitures". This is true even though the pieces of furniture comprising "furniture" could be counted. Thus the distinction between mass and count nouns shouldn't be made in terms of what sorts of things the nouns refer to, but rather in terms of how the nouns present these entities. 
See main article: Collective noun. Collective nouns are nouns that refer to groups consisting of more than one individual or entity, even when they are inflected for the singular. Examples include "committee", "herd", and "school" (of herring). These nouns have slightly different grammatical properties than other nouns. For example, the noun phrases that they head can serve as the subject of a collective predicate, even when they are inflected for the singular. A collective predicate is a predicate that cannot normally take a singular subject. An example of the latter is "talked to each other".
Good: The boys talked to each other.
Bad: *The boy talked to each other.
Good: The committee talked to each other.
See also: physical body and abstract object. Concrete nouns refer to physical bodies which you use at least one of your senses to observe. For instance, "chair", "apple", or "Janet". Abstract nouns on the other hand refer to abstract objects, that is ideas or concepts, such as "justice" or "hate". While this distinction is sometimes useful, the boundary between the two of them is not always clear; consider, for example, the noun "art". In English, many abstract nouns are formed by adding noun-forming suffixes ("-ness", "-ity", "-tion") to adjectives or verbs. Examples are "happiness", "circulation" and "serenity".
Noun phrases can typically be replaced by pronouns, such as "he", "it", "which", and "those", in order to avoid repetition or explicit identification, or for other reasons. For example, in the sentence "Janet thought that he was weird", the word "he" is a pronoun standing in place of the name of the person in question. The English word one can replace parts of noun phrases, and it sometimes stands in for a noun. An example is given below:
John's car is newer than the one that Bill has.But one can also stand in for bigger subparts of a noun phrase. For example, in the following example, one can stand in for new car.
This new car is cheaper than that one.
Starting with old Latin grammars, many European languages use some form of the word substantive as the basic term for noun. Nouns in the dictionaries of such languages are demarked by the abbreviation "s" instead of "n", which may be used for proper nouns instead. This corresponds to those grammars in which nouns and adjectives phase into each other in more areas than, for example, the English term predicate adjective entails. In French and Spanish, for example, adjectives frequently act as nouns referring to people who have the characteristics of the adjective. An example in English is:
The poor you have always with you. Similarly, an adjective can also be used for a whole group or organization of people:
The Socialist International. Hence, these words are substantives that are usually adjectives in English.