The Morpheme: Its Nature and Use

1 Some Background
In linguistics, morphology is the study of words, and since the morpheme is at the core of morphology, we begin with the basic notion of a word. Although notoriously subject to differences of sense when seen from different perspectives, a word is fundamentally the unit of mutual association among several sorts of properties. _us, the word cat in English has phonological properties, semantic properties (‘Felis catus, a small furry domesticated carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests’) and syntactic properties (Noun, [+Common, +Count]). The connections among these are irreducible: that is, it is not possible, say, to associate the vowel // by itself with the ‘cute, furry’ part, or the final /t/ with its status as a common (not proper) Noun.
1.1 Origins: Signs, Basic and Otherwise
As such, cat nicely fits de Saussure’s (1916 [1974]) notion of a minimal linguistic sign (even though Saussure did not include syntactic content in his account of individual signs). But Saussure realized that not all words are minimal signs. Even ignoring the problems presented by phonological words that include clitics together with their hosts (for which, see Anderson 2005), a word like unavoidable has a rather different character from that of cat._The phonology here is something like “avoidable" the semantics more or less ‘not possible to avoid’ and the whole thing an Adjective. In this case, parts of the phonology are connected to parts of the meaning, so the initial /an/ represents the ‘not’ part, the final /bl"/ the ‘possible to’ part, and /@void/ the ‘avoid’ part. Such a word Saussure called a