the same variation (or allomorphy) in the shape of the stem as in application. These patterns show us that the derivational whole may be more than the simple sum of its parts.
When we consider the class of adjectives in –able (or its spelling variant –ible), we find a number of forms like credible, eligible, potable, probable,… which seem to have the right meaning for the class (they all mean roughly ‘capable of being [SOMETHING]-ed’), but the language does not happen to contain any verb with right form and meaning to serve as their base. This suggests that derivational patterns have a sort of independent existence: they can serve as (at least partial) motivation for the shape and sense of a given lexeme, even in the absence of the possibility of deriving that lexeme from some other existing lexeme. In some instance, the force of this analysis is so strong that it leads to what is called back-formation: thus, the word editor was originally derived from Latin e:dere ‘to bring forth’ plus –itor, but it fit so well into the pattern of English agent nouns in –er (e.g., baker, driver) that a hypothetical underlying verb edit actually became part of the language.
We may also notice that some –able forms do not mean precisely what we might predict. Thus, comparable means `roughly equal’, not just ‘able to be compared’. In the world of wine, drinkable comes to mean ‘rather good’, not just ‘able to be drunk’, etc. This shows us that even though these words may originally arise through the invocation of derivational patterns, the results are in fact full-fledged words of the language; and as such, they can undergo semantic change independent of the words form which they were derived. This is the same phenomenon we see when the word transmission, originally referring to the act or process of transmitting (e.g., energy from the engine to the wheels of a car) comes to refer to a somewhat mysterious apparatus which makes strange noises and costs quite a bit to replace.
Finally, we can note that in some cases it is not at all evident how to establish a ‘direction’ of derivation. In Maasai, for example, there are two main noun classes (‘masculine’ and ‘feminine’), and a derivational pattern consists in taking a noun which is ‘basically’ of one class, and treating it as a member of the other. Thus, en-kéráí is a feminine noun that refers to any child, of either gender; while ol-kéráí is a corresponding masculine noun meaning ‘large male child’. Here it looks plausible to take the feminine form as the basis for the derivational relationship; but when we consider ol-abáánì (masculine) ‘doctor’ vs. enk-abáánì ‘small or female doctor, quack’ it looks as if the direction of derivation goes the other way. In fact, it looks as if what we have here is a case of a relation between two distinct patterns, where membership in the feminine class may (but need not) imply femaleness and/or relatively small size, as opposed to the masculine class which may imply maleness and/or relatively large size. When a word in either class is used in the other, the result is to bring out the additional meaning associated with the class, but there is no inherent directionality to this relationship. The possibility of back formation discussed above suggests that this interpretation of derivational relationships as fundamentally symmetrical may be applicable even to cases where the formal direction of derivation seems obvious.
Compounding
The other variety of word formation, compounding, seems fairly straightforward, even if the actual facts can be quite complex at times. Compounds are built of two (or more) independent words, and have (at least in their original form) a meaning that involves those of their components. Thus, a catfish is a kind of fish sharing some property with a cat (in this case, the whiskers). Like derived forms, compounds are independent lexemes in their own right, and as such quickly take on specialized meanings that are not transparently derived from those of