People have found this text useful so I am repeating it here in this entirety with error fixed (there are several posts combined in it)

Before I give you more detailed explanation I have to tell you that in dictionaries you can frequently find the type of the word: countable, uncountable, mass, abstract… However what is more important is to understand that the context is equally important. You can turn many words into abstract if you want to express an idea, quality or experience, and you can as well make from an uncountable word a countable one if you want to speak about one particular appearance… So before you decide what is the type of the word you have to know

  • what is the most frequent context in which the word is found
  • what are the contexts you can use the word
  • whether and how each context changes the meaning of the word
  • which context is maybe awkward for the particular word

  • Once you know the context you can decide about the article attached. So here you have all contexts that one word can be found in. Do not forget that it is possible that you can change the context even when your dictionary says that a word is, for example, strictly countable.

    A ball can mean one instance of ball, a more or less round gadget of different materials for playing games, but ball can mean the experience of playing games with a ball.

    • A ball is usually round. - one ball
    • Ball, however I've loved it, is what hurts my knees. - the experience of playing different games with a ball

    • However, this is the advanced level of understanding and for some time you should be very strict and use words how they are given in the dictionary. But, in order to truly understand some exceptions in literature you have to have the following view better.

      1. The possible contexts of a word

      count nouns one ball-two balls-some balls

      • they have plural
      • in singular you have to use a/an or the
      • in plural you use the to define a particular instance, and without the to define a type

      • uncount nouns homework-fun-knowledge-privacy-furniture

        • they have singular but it is used, by the rule, without a/an
        • they do not have plural
        • you do not count them using one, two... but you can measure them using some, a piece of…

        • mass nouns coffee-beer-cheese

          • in singular they can mean substance and in that case they are uncount so you do not use a but if you use the you mean a particular kind of that substance
          • in singular you can use a but in that case you talk about a regular portion or a type, a is actually a substitute for one (I want a coffee = I want one coffee = I want one cup of coffee)
          • in plural they mean several regular portions or types (several different cheeses = several different type of cheeses, two coffees = two cups of coffee)

          • singular nouns sun-strain-past-future

            • they are always singular and they always need a determiner (the sun, a strain, the past)
            • some normal nouns may have a special meaning when they are used as a singular noun (a note of urgency = a tone of haste)

            • plural nouns glasses-spectacles-clothes-conditions

              • they have only plural and you do not usually count them, but there are exceptions (two goods is not common, two scissors is ok)
              • you can use only the for known occurrences, for other the rules are similar to an uncount noun, unless you can count them (a/one scissors but even then you better say some scissors, a pair of scissors)
              • some normal words may have a different meaning when used as a plural noun (conditions - the factors that affect something)

              • collective nouns army-crew-government

                • they behave as a count noun but they can use singular or plural verb form, which depends on how you observe a group - as one item or a collection of several items
                proper nouns names

                • they have the or do not have the based on the special rules or simply a custom
                compound nouns

                • they are the nouns made of several words
                • apart from that they can belong to any other group mentioned here
                • they have special rules of creating the plural

                • abstract nouns intelligence-joy-relief

                  • abstract nouns are usually uncountable and they behave as one
                  • if you count them or use plural, you are referring to particular instance(s)

                  • We choose our joys and sorrows long before we experience them. (joys - the things that make us joyful)

                    concrete nouns the nouns that are referring to physical objects

                    • they can be in any group said above except abstract
                    As you can see the rules are strict, but there are exceptions. We say that uncountable nouns you cannot count, they do not use a and have no plural. However, if the word belongs to an abstract group expressing idea, feeling or experience, it may still be counted and have the plural when you mean about the particular occurrence(s). Not all abstract words are capable to switch to plural.

                    Some words can be observed as uncountable (hair) and behave as one, but if you use a they change the meaning. hair - strands growing on head or body, a hair - single strand growing on head or body (or found in a soup) However, you can see that a is used to restrict the occurrence to certain physics dimension. Not all uncountable words are capable to use a and to be counted. If they do they almost without an exception change the meaning, though sometimes the change is not very serious.

                    water is uncountable so the rules says no plural, but then you deprive yourself from some important possible usages or understanding

                    waters -

                    • a type of mineral waters
                    • all rivers that flow into a large river or cover certain region
                    • drops
                    • place(s) to practice water sports
                    • the places covered with water on the Earth
                    • an area, realm (it can leads us to unknown waters)
                    • the water natural beauties like waterfall, cascades...
                    • a spa
                    • the water near the shore of region or country
                    • a type of water coming from many different sources - toxic waters

                    • a water -

                      • a river or lake or any closed area covered with water
                      • a small amount of water that was examined for purity
                      • a drop

                      • So uncountable water is very capable to switch to a countable case with, of course, change of the meaning. Thus, the entire previous detailed classification is frequently relative. (However, when you use words in their regular and natural and most common context you use the strict rules: furniture in my house, not furnitures in my house, unless you have all together Louis XV, Louis XVI and Louis XVII furniture in your house [furnitures - types of furniture] to show off around. The furnitures we have are: commercial use furniture, counter system furniture, job station furniture, retail counter furniture)

                        I hope you start getting a picture. However, before you go into this area more thoroughly, it is highly recommendable to follow the standard usage especially if you have kind of exam.

                        The most frequent case is that each word has many different meanings. Each meaning can belong to a completely different group of words. A good dictionary gives the classification not by the word, but by each meaning of the word.

                        Sometimes you have to guess the classification, which is normally not so difficult.
People have found this text useful so I am repeating it here in this entirety with error fixed (there are several posts combined in it) This is the effort of Mister Micawber as well.

The rules given in many textbooks are based not on the general rules but on the frequent omissions. (advice is uncountable, homework as well; sometimes these rules are given only because other languages treat these words as countable)

It can be confusing because you are focused only how not to make errors instead to learn what is the true reason of using a, the or not using them. These rules are very simple and very logical, for example, you do not use a/an with abstract nouns because you usually do not count quality, experience, feelings…: one happiness, two happiness???, no! two happinesses; unless you really want to say something special about it. (For example: My children are my two happinesses.)

2. The plural of abstract nouns

When the word is derived using, for example, ness (busy+ness = business) to create the plural the strict grammar requires +es. Many abstract nouns of this sort are anyhow rarely used and even more they really do not have plural and some of them are difficult to pronounce - so what you are doing is applying the general grammar rules used to derive the plural form of a noun, regardless of the possible artificiality of your final result. If for any reason you need the plural form you should have

  • luckiness - luckinesses
  • pleasantness - pleasantnesses
  • fearlessness - fearlessnesses
  • vigorousness - vigorousnesses
  • willingness - wilingnesses

  • regardless of how difficult it could be to pronounce. (Of course not all abstract nouns have ending ness. Then, you follow the normal rules for plural: add , or change +s, .)

    Thus, you should always use +(e)s for plural. However, it is possible that the plural without +es has the specific and accepted meaning that is exactly what you need or maybe not what you need. Or, it can happen that plural (+es) means something specific you do not need to allude in your text at all. Not only that, adding +es to the abstract noun can have a very jocular or sarcastic tone. So you should think if the plural is good at all. Here is one example:

    They don't send money for such secular unholinesses like WATER, FOOD, BLANKETS. No; they only send money for extremist mosques, militias, missionaries, and madrassas [sic].

    Here, the writer is very angry that they do not send money for, for them, completely unimportant essentials, but, as if that is only what their religion is/were about, they think only about the armory and the war.

    So be careful with abstract nouns in plural. Just to give you more examples where plural and singular of the abstract nouns are important

    • holiness - the state or quality of being holy
    • holiness - spiritual or religious leader (usually the Pope or other high bishop or episcope)
    • holinesses - different states or quality of being holy
    • holinesses - spiritual or religious leaders (their holinesses)

      • His Holiness - usually the Pope
      • Their Holinesses - several spiritual leaders
      • Their Holiness - again the Pope or other leader, but addressed with higher admiration

      • If the reason of difficult pronunciation is why you do not like to add :

        cholinesterases, comradelinesses, consideratenesses, heartsicknesses, intricatenesses, irasciblenesses, lucrativenesses, mercenarinesses

        all perfectly acceptable English words. My throat is hurting hard of just looking at these words.[:^)] Yet, they are fine.

        [sic] - meaning: though not correct this is how it is found in the text