Correct grammatical number of items belonging to a group, e.g.. ‘Every person has a nose.’ [duplicate]

Solution 1:

This question has an answer in § 5.37 of A comprehensive grammar of the English language.

The particular usage in this entence is not the so-called generic use.

(CoGEL 5.53) The generic use of the indefinite article

The generic use of a/an picks out ANY REPRESENTATIVE MEMBER OF THE CLASS. Thus any can be substituted for a/an in examples like:

♦ The best way to learn a language is to live among its speakers.

Generic a/an is therefore restricted in that it cannot be used in attributing properties which belong to the class or species as a whole. Thus:

♦ The tiger is becoming almost extinct.
♦ Tigers are becoming almost extinct.

BUT NOT: *A tiger is becoming almost extinct.

If the principle of substitution of "any" is applied, the result is wrong, so this use is not the generic use.

• Everyone has any nose.

The particular usage of the indefinite article in the query has a somewhat indeterminate nature, that, perhaps grammarians still have to categorize more neatly. Here is § 5.37 from CoGEL to confirm this fact.

(CoGEL § 5.37) Nonreferring uses of the indefinite article
The indefinite article is strongly associated with the complement function in a clause, or more generally with noun phrases in a copular relationship. Here it has a descriptive role (similar to that of predicative adjectives), rather than a referring role:

• Paganini was a great violinist.
• My daughter is training as a radiologist.
• We found Lisbon (to be) a delightful city.
• What a miserable day (it is)!

Whereas the indefinite article is required in the previous examples, there is vacillation in the following cases:

• her duties as (a) hostess
• my appointment as (a) lecturer
• Jung as (a) thinker

Sometimes a/an is nonreferring in a stronger sense; it may not refer to anything in reality at all:

• Leonard wants to marry a princess who speaks five languages.

From this sentence, we cannot tell whether Leonard knows a certain princess and wants to marry her, or whether he has simply laid down exceptionally stringent qualifications for his future wife. For all we know, there may be no princess who speaks five languages in existence.

In the following sentence, which would have to be from a horror story, the use is clearly referring.

They walked along the canal, when something caught his glance on the ground… it was a nose, yes a nose, smeared with blood that wasn't dry yet; it was a full nose, cut neatly at its root up to the bridge.

In "Everyone has a nose", this is clearly not so. The authors of the CoGEL speak of a descriptive role in association with the complement function. Here, "has" does not introduce "nose" as a complement but as an object; nevertheless, saying that everyone has a nose amounts to describing everyone, at least to some extent, and so I believe that this use of "a" is descriptive or, put in another way, defining.