If we look at the system of noun classes in African languages, we see that not all noun classes are productive. Briefly explain the difference between productive and non-productive noun classes.

Productive noun classes are those that are actively used and can be applied to new nouns in the language. These classes are still in use and can be easily extended to include new nouns. Non-productive noun classes, on the other hand, are no longer actively used in the language or have limited application to new nouns. These classes may have become obsolete or are only used in specific contexts or with a limited set of nouns.

Productive Noun Classes:

- Can form new nouns by adding derivational affixes (e.g., prefixes, suffixes).
- Allow for the creation of new nouns to fit emerging concepts or specific contexts.

Non-Productive Noun Classes:

- Do not allow the formation of new nouns through derivational affixes.
- Have a fixed set of nouns that belong to them.
- Typically represent basic concepts or categories (e.g., humans, animals, places).