This section provides a classification of common nouns. The basic semantic distinction to be made is that between concrete and abstract nouns (which can also be made in the case of proper nouns; cf. (23)). Concrete nouns are usually defined as nouns denoting “tangible” objects (i.e. that can be seen or touched), whereas abstract nouns denote “non-tangible” entities such as processes, phenomena, emotions, properties, etc.; some classifications therefore include nouns like geursmell and geluidsound in the set of abstract nouns. We will not follow this and define concrete nouns in terms of physical existence: the class therefore includes nouns denoting entities that can be heard, tasted, or smelled, or in some cases only indirectly observed (e.g. microbes, gases, black holes, and force fields). The categories of concrete nouns can be shown to consist of a number of subcategories, which are discussed in Section 15.2.2.1; the same will be shown for abstract nouns in 15.2.2.2. It is possible for concrete nouns to be used as abstract nouns, and vice versa; such non-prototypical uses (sometimes called “conversion”) are also dealt with here.