The Swahili noun classes have differing degrees of internal coherence in their semantic structure. At one extreme are Classes 1/2, often called the `human' classes, whose membership consists almost entirely of nouns denoting human beings, especially agents of actions. At the other extreme are Classes 9/10, which have absorbed the majority of foreign loanwords, and may already have been fairly heterogeneous even before the major influx of loans from Omani Arabic, dating only from the 17th century (N + H 1993:320). In this section I will propose an analysis of the classes that fall in the middle, the ones that constitute the nucleus of the system.
4.1 Class 3
Figure 1 is a schematic representation of the semantic structure of Class 3.
The top-to-bottom organization of the diagram moves from the more general to the more specific, but the diagram is not intended to be a `taxonomy' in the technical sense (cf. Casson 1981:75-77). I have borrowed the conventions used by Langacker (1988) for the representation of a linguistic category. Langacker defines two basic types of semantic relationship among the elements in a category:
(a) relations of `schematicity', in which one element is an `elaboration' or `instantiation' of another, more abstract element (represented by solid lines in the diagram); (b) relations of `extension', in which some feature specifications are suspended or modified, while other features are retained (represented by dotted lines in the diagram).
Examples of nouns in each category  may be viewed by clicking on the relevant area of the diagram.
This analysis incorporates many of the insights and observations of earlier studies of Swahili, such as Ashton (1944:23), Polome (1967:97), Hinnebusch (1979:230), Zawawi (1979:chapter 5); Meinhof (1948 :28-64) anticipated many of these in his comparative grammar of Bantu. What I have tried to do here is make explicit the connections among the various semantic categories that had been identified by others, and add some categories that have not been mentioned before.
The topmost category in the chart, `entities with vitality', is what Langacker (1988) calls a `superschema', a maximally abstract category that holds together the various subcategories. `Vitality' is meant to capture various attributes of living beings, including growing and reproducing (true of plants, and metaphorically of human collectivities), but also ability to move (active body parts), to act on or affect other entities in the world or to occur independently of human volition (supernatural and natural phenomena).
The categories `exceptional animals' and `human collectivities' require some additional comments. These categories appear to be in this class not only because of properties that they share with other members of the class, but also because of the opposition between this class and other classes in the Swahili noun class system. First, the animals. In Swahili, as in other Bantu languages, most terms denoting animals are in Classes 9/10. These can be thought of as the `default' classes for animals, especially mammals, virtually all of which are in 9/10 in Swahili. All animal terms that are not in 9/10 are therefore exceptional in some way. If one looks at the distribution of animal terms outside 9/10, the situation is as follows:
(a) those in Classes 1/2 (the `human' classes) are either generic terms for whole groups of animal species, agentive nouns, or terms derived from Class 1 nouns (already pointed out in note 8); (b) those in Classes 7/8 denote small animals (see chart of Class 7, below); (c) those in Classes 5/6 denote either animals that are large for their type (such as kunguru `carrion crow', panzi `grasshopper', moma `puff adder'), or non-mammals (e.g. kaya `kind of shellfish', tekenya `jigger, burrowing flea').
The animal terms that are in Class 3 are unusual because they do not fit easily into established categories, either because of their appearance (swordfish), their behavior (kingfisher, Golden Weaver finch, termite, cuttle-fish), or a combination of these (the eel is like a snake, but also like a fish; leeches and intestinal worms have an unusually intimate relationship with the human body-- and mjiko `lower bowel' is also in this class, so metonymy could also be operating here).
The case of human collectivities is somewhat similar. These are entities that include human beings, but are not themselves human, so they fall somewhere between animate and inanimate. Class 3 is a compromise: it has a human-like prefix (m-), but a non-animate agreement pattern.
Among all the subcategories of Class 3, that of plants/trees can be regarded as the most central, for several reasons. First, this subcategory contains the largest number of terms (almost half of all the nouns in the class). Second, it is productive in two ways: loanwords denoting trees and plants are almost always assigned to this class regardless whether the term in the source language had an initial m-; trees and plants form the model for the majority of metaphoric and metonymic extensions in Class 3.
The subcategories below the second level on the diagram are interrelated in several ways: many terms fit with equal ease into the subcategories `extended things', `active things', `extended parts of things', and `objects made of plants'. My objective here is to suggest plausible avenues for semantic extensions; these need not be mutually exclusive. To the extent that a term fits into more than one category, it can also be regarded as well-entrenched within the semantic network of Class 3.
The most salient aspect of trees and plants, from the point of view of the subcategories associated with them, is shape, i.e. extendedness in one dimension. This physical attribute is the basis for the inclusion in this class of some inanimate objects not made of plants, such as `nail', `ramrod', `metal chain', and of extended body parts of humans and animals (`bone', `blood vessels', `sinew', `porcupine spine', etc.). The inclusion of objects made of plants (`wooden platter', `straw mat', etc.), on the other hand, is based on metonymy.
The inclusion of long body parts in Class 3 motivates a further extension, by metonymy, to coverings that are wrapped around the body. This seems to be a recent extension within Swahili: none of the nouns in this group are reconstructed for Proto-Sabaki or Proto-Swahili by N + H, and some of them are loanwords from Arabic (but significantly, these did not originally begin with m-).
The category `powerful things' includes inanimate objects that have effects on human beings, such as substances with curative properties or religious objects. Some of these are made of plants, so they are connected both to this and to the category `supernatural phenomena', since they derive their power from some agency other than human. `Active things' are things, especially tools, that have movement as a salient characteristic: `arrow', `pestle', `chopper', `loom pedal', etc. In contrast to the `powerful things', they must be set in motion by a human agent. In this way they are similar to the `active body parts', which move but do not have independent volition.
Perhaps the most abstract distillation of the `entities with vitality' category is the use of Class 3 to derive deverbal nouns referring to the verbal process itself, such as mparuro `a scratching' (from -parura `to scratch'), mfuo `a hammering' (from -fua `to hammer'), mlio `a sound' (from -lia `to make a sound'), etc. Such nouns describe a process as a thing, and so fit well with the other liminal entities in this class, that fall somewhere between animate and inanimate. [Section 4.2]