I am quite confused about the usage of countable nouns and singular countable nouns. I would like to know about their usages. I will try to explain those with some examples.
1. Knowledge: In dictionaries the type of noun is given as uncountable and singular. It can be singular in following instances:
A strong knowledge of computer or a knowledge of carpentry.
Actually, we can’t measure knowledge – 1 knowledge, 2 knowledge, etc.
Let’s take another example: life or work
Life: Per dictionary, it’s an uncountable noun as well as a countable noun. But, I have heard lots of people saying, you are living a good life. If you set this example against the first one, then you can see the difference. Life is countable, and we can use an indefinite article and knowledge is a singular noun and we can use an indefinite article.
1. You are living a good life.
After contemplating it more, I am now assuming we can use an indefinite article if it is a countable or singular countable noun. But, if we consider work, it is more used as an uncountable noun. Sometimes it is used as a countable noun too. If it is used as a countable noun, then why can’t we say –
1. You are doing a good work.
However, we can say “a work in progress”.
Similarly with “fruit” and “food” -
Give me a fruit or give me fruit or give me some fruits.

Can someone elucidate the difference to me? Or Should I have to check their usages before using them in sentences?
harry1999I am quite confused about the usage of countable nouns and singular countable nouns.
I can sympathize with your problem. Your question touches on some very advanced concepts in English grammar.

The problem is that nouns are not as simple as your less advanced grammar books would like you to believe. It is not literally true that nouns can be divided into countable nouns and uncountable nouns. According to at least one grammarian, there are five degrees of countability that can be observed in English nouns, ranging from fully uncountable to fully countable. (And for some reason, he splits one of the degrees into two subclasses, for a total of six kinds of nouns.) From fully uncountable to fully countable, these are the classes:

Degree ............. Example .......................... Permitted Determiners
I ........................equipment .................................NONE
IIa .....................knowledge...................................a
IIb......................clothes........................................many, few
III.......................cattle..........................................many, few, and relatively large round numbers
IV.......................police.........................................ALL EXCEPT those listed below*
V........................dog............................................ALL

*this, that, a, another, either, neither, each, much, less, a little, every, little, one
(Rodney Huddleston, Introduction to the Grammar of English.)

I don't know of other ways of classifying these, but there are most likely other grammarians who would build a different classification system. In any case, the chart above doesn't really tell us how to use the determiners with the nouns; that is, even if we know that a can go with knowledge, we still don't know (from the chart) when it should go with knowledge and when it shouldn't.
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Unfortunately, there is no dictionary in existence (that I know of, anyway) that lists nouns together with this kind of information. And worse yet, I have no doubt whatsoever that most native speakers of English would be very hard pressed to classify a given noun in this way unless it were of degree I or V. I have my doubts about how useful such a chart can be to learners of English because it so often happens that the same word can be used in more than one way. For example, work can be used with all determiners in one context or another, so it's in class V, but that tells us nothing about the usages where it acts like a class I noun.
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I don't know if this helps you or not, but at least it gives you some idea of how complex the topic is, and it can therefore give you a way of seeing that it is very difficult for any of us to give you any definitive answers to your questions.

CJ
"IIa .....................knowledge...................................a"

Is the determiner "some" permitted to collocate with knowledge ?
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AnonymousIs the determiner "some" permitted to collocate with knowledge ?
Yes.

Use the link below and open page 245. Huddleston gives a list of determiners at (22) that includes "etc.", so it turns out he hasn't listed every possibility in his chart.

http://books.google.com/books?id=irXAKZSHc38C&q=countability+and+boundedness#v=snippet&q=countabi...

CJ
Thank you, CJ, for your useful reply.
It's really helpful. The example shown for "equipment" makes me confused. From the chart, the noun equipment is an uncountable noun and it does not take any determiner. But, in the given examples it is seen he has used "a good equipment" Shouldn't it be "some" or "any" equipment. The examples I used in my questions are from Merriam Webster's advanced learner's dictionary. If you see the word "knowledge" in the dictionary, you can see they have used "a" before knowledge and its kind is singular countable noun. But for "life" it does not work even though we can say "a good life".
Pity! Emotion: rolleyes
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harry1999in the given examples it is seen he has used "a good equipment"
Are you sure you know the difference between these?

*a good equipment
a good equipment

An asterisk ( * ) means that the phrase, clause, or sentence is not grammatical.

I believe he gave *a good equipment as an example, not a good equipment.

CJ
The following is US usage.

The word "knowledge." There is no such word as "knowledges." Knowledge can have an implied plural sense, as in the sentence: "He has knowledge of many different subjects."

The word "life." There is no such word as "lifes." The plural of "life" is "lives."

The word "work." In the sense of labor or profession, there is no such word as "works." However, there can be an implied plural sense, as in the sentence: "The work I've done in is in the fields of banking, accounting, real estate, and retail management." In the sense of items of art, literature, or charity, there is a plural, "works," as in: "These are the most famous of the artist's works."

As for the use of articles with the words knowledge, life, work, fruit, and food, there are innumerable situations. These can't be covered by a few rules, and one must learn them by experience.

For example, the sentence, "You are doing a good work.", is incorrect in the sense of labor, but it is okay in the sense of charity.

"You are living a good life." is correct, as is "You are living the good life." But "You are living good life." is ungrammatical.

"He has a strong knowledge of computer." and "He has a strong knowledge of a computer." are ungrammatical. It has to be "He has a strong knowledge of computers." or "He has a strong knowledge of the computer."

"He has a knowledge of carpentry" and "He has knowledge of carpentry." are correct. "He has the knowledge of carpentry." is apparently okay, but sounds archaic and stilted. "He has knowledge of the carpentry." is ungrammatical, but you can say "The carpentry in this building is excellent."
Oh, thank you CJ for the reply. I thought it was used as a correct example. I understood now.
Thank you.
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