We know about the classification of words in languages like Yagua because of grammatical markers called classifiers that indicate the type or “class” of noun involved. For example, in Swahili (spoken in East Africa), different prefixes are used as classifiers on nouns for humans (wa-), non-humans (mi-) and artifacts (vi-), as in watoto (“children”), mimea (“plants”) and visu (“knives”). In fact, a conceptual distinction between raw materials (miti, “trees”) and artifacts made from them (viti, “chairs”) can be marked simply by the classifiers used.

In the Australian language Dyirbal, traditional uses of classifiers indicated that “men, kangaroos and boomerangs” were in one conceptual category while “women, fire and dangerous things” were in another. Exploring cultural beliefs (e.g. “The sun is the wife of the moon”) can help us make sense of aspects of an unfamiliar world view and understand why the moon is classified among the first set and the sun among the second.

Classifiers are often used in connection with numbers to indicate the type of thing being counted. In the following Japanese examples, the classifiers are associated with objects conceptualized in terms of their shape as “long thin things” (hon), “flat thin things” (mai) or “small round things” (ko).

The closest English comes to using classifiers is when we talk about a “unit of” certain types of things. There is a distinction in English between things treated as countable (shirt, word, chair) and those treated as non-countable (clothing, information, furniture). It is ungrammatical in English to use a/an or the plural with non-countable nouns (i.e. *a clothing, *an information, *two furnitures). To avoid these ungrammatical forms, we use classifier-type expressions such as “item of” or “piece of,” as in an item of clothing, a bit of information and two pieces of furniture. The equivalent nouns in many other languages are treated as “countable,” so the existence of a grammatical class of “non-countable entities” is evidence of a type of cognitive categorization underlying the expression of quantity in English.