Many learners' dictionaries note whether a noun is countable or uncountable. For example: http://dictionary.cambridge.org/ (look up the learner version). Uncountable nouns can normally be used with "the" but not usually with "a/an" e.g. Love is a wonderful feeling (in general). e.g. The love that I have for my wife (this particular love) is special. e.g. Water is essential for life (in general). e.g. The water in the Pacific Ocean ((this particular amount of water) is salty.

The countability of English abstract nouns can be a toughest problem for Chinese English-learners. I myself feel difficulty identifying it of an abstract noun. So very often when I use one, I refer to learner's dictionaries. I have once tried to dig deep into the Number of English and tried to find the ultimate rules or notions in the mind of native English speakers about when an abstract noun can be countable ans when not, I failed--naturally: even some greatest English grammarians or teachers have failed to solve this problem. In fact, maybe this is not a solvable problem, because it's very common that there are two nouns which come into the same category while, one is countable and the other not. repute: uncout. reputation: uncount. and single ( but quite a few learner's dictionaries mark it as C/U, or enven just C [longman]; and even one and the same dictionary sometimes deal with two nouns in the same type in inconsistant ways. This is a big trouble for learners because it may get them[us] bewildered.) allegation: count. and often in pluaral. Maybe we can draw a conclusion that the countability of an abstract noun bases on two factors: 1) the logic of the reality of the world: certain abstract nouns appear only or offen in a particular context where its countability is reasonable 2) but there are still unreasonable cases: some abstract nouns correspond to the certain concepts in the natives's mind, and those concept may be disdinctly differently in another nationa's mind, and this is the very reason that makes English learners uncertain whether an abstract noun may be countable.