For instance,
"I don't have time to do this." Here, the noun "time" is uncountable.
"I had a great time." In this case, is the noun in the noun phrase "a great time" countable?
IS there any systematic way to explain the concept behind this? According to several grammar books I looked into, uncountable nouns can be preceded by an article "a" when modified or specified. But WHY?
Also, some nouns are more often used with "a" and others are rarely. For instance, "knowledge
" is almost always preceded by "a" when modified, as in "He has a great knowledge of English grammar." But "information" is rarely used with "a" even when modified. For example, it's usually just "valuable information", rather than "a valuable information." Please tell me why!

Thank you very much.
Hello Infinity.

I'm a mere English learner from Japan, but could you allow me to throw my 2 cents on your question?

Frankly speaking, I'd say you'd better give up the hope you could get a conclusive answer to the question. I have raised a similar question before in this forum but I could not get enough persuasive responses (He has a good English).

As for some nouns (especially substantive nouns), English distinction between countable/uncountable seems mostly reasonable cross-linguistically. But for some nouns (above all abstract nouns), the distinction cannot be logically understood to non-native English speakers. I think we should take this kind of distinction as a matter belonging to the realm of linguistic habit particular to English rather than to the realm of universally available reasons. Countableness for some nouns is different even between similar European languages. For example, "information" is deemed as uncountable in English but it is countable in French and German. So I think we had better learn English's countableness of nouns without asking why it is so. ([url="http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv192.shtml "]BBC grammar QA[/url]).

Nevertheless, I'd like to add about your question what I feel personally. I think English people someway has a tendency to take a thing as countable in the case they could feel there would be things similar to that thing. For example, let me take the case of "knowledge". When you say "knowledge" without adding the indefinite article "a", it means a general and indefinable amount/sort of "acquaintance with something through experience and intelligence". But when you say "He has a knowledge of biology", the noun phrase "a knowledge of biology" is interpreted to imply "a certain sort/amount of knowledge on biology such as that you can imagine other people also might have one similar to that. It is my humble opinion.

Anyway as I'm a beginner of English learning and don't know much about English, you'd better not believe me so much. Our teachers and other native speakers must give you much much better answers. Please wait until then.

uncountable nouns can be preceded by an article "a" when modified or specified. But WHY?

Because we want to talk about something very specific and definite .

"I had a great time" -we are specifying the particular time I spent doing that partcular thing

"The supermarket is full of groceries " - "I bought some groceries" (not all of them)

"Knowledge is a great thing" - here we are refering to 'knowledge' in its broad general sense, which is uncountable.

"Infinity hopes to gain a good knowledge of uncountable nouns" - here we are specifying the exact type of knowledge Infinity wants.

"Information" can be preceded by 'a', but you need to specify or quantify it:

"He gave me a valuable PIECE of information"

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Thank you very much, both of you.
The knowledge and information you provided for me are truly helpful.
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