When writers use a noun to talk about something specific, they know what they are referring to. But they must consider whether the reader will also know. We saw above that a writer can use any noun (count or non-count, singular or plural) to refer to something specific. Sometimes the reader knows what the writer is referring to. Sometimes the reader does not know.
Specific and Known Versus Specific and Unknown
Here are some examples that contrast nouns that are specific and known (to the reader) with nouns that are specific but unknown (to the reader):
The Great Lakes contain fresh water, not salt water.
(Lakes = count, specific, and known)
We camped by some beautiful lakes last summer.
(lakes = count, specific, and unknown)
The equipment in the Photo Lab is all new.
(equipment = non-count, specific, and known)
We got some new equipment in yesterday.
(equipment = non-count, specific, and unknown)
Ensuring That A Specific Noun Is "Known"
There are several different ways that writers can be confident that readers will know what they are talking about or, in other words, that a specific noun can be "known."
FIRST, writers may be talking about something that is unique. Compare, for example, the following two sentences. In the first sentence, the house referred to is a unique white house, specifically the residence of the President of the United States. It is unique and known to readers, unlike the unknown white house referred to in the second sentence.
The White House stands on Pennsylvania Avenue.
I live in a white house.
SECOND, writers may rely on a readers' common sense or general knowledge to know exactly what they are talking about. Compare, for example, the following two sentences:
The college bookstore closes at 9:00 P.M.
I bought this book at a downtown bookstore a few days ago.
THIRD, writers can assume that readers will know exactly what they are talking about if they have already mentioned it:
I got a new car and a new bike last week. My wife doesn't like the car very much.
FOURTH, writers can add identifying information immediately after a noun so that readers will know what they are talking about. Compare, for example, the following three sentences:
The green house on Main Street belongs to my friend.
The green house where I grew up has been demolished.
Marcia lives in a green house.
The houses referred to in the first two sentences are made known to readers through the use of the identifying information, on Main Street and where I grew up. The house mentioned in the third sentence is not specifically known to readers because there is no identifying information provided.