Countables and uncountables

Some nouns can be counted—we term these countable; other nouns cannot—we term these uncountable. By and large this distinction makes sense in terms of how we humans view the real world. Thus, for example, horses are countable, while flour is obviously not. Such cases are generally not a problem. However, there are entities that are, from a human perspective, on the borderline, which do cause problems for learners of English. Take clouds and fog, for examples. Some days you can count clouds and some days you can’t, but nonetheless we treat clouds as if they were always countable—one cloud, two clouds, and so on. Fog, however, is a different story, despite not being too much different from clouds, at least from a real world perspective. Fog we treat as uncountable; we cannot say *one fog, *two fogs, and so on. Thus, from the perspective of the grammar of English, clouds are countable, but fog is not.