A phonological alternation which is conditioned by a significative contextual factor is morphologized if it persists despite the loss of the conditioning factor. This process is little documented from historical languages. The only standard example is, in fact, the morphologization of metaphony in Germanic languages. It plays a considerable role in German, but will here be illustrated from English.

In this example, morphologization is prepared by three purely phonological processes. In the Germanic languages, metaphony starts out as a regular phonological process of vowel harmony. Roughly, a vowel becomes a front vowel if the following syllable has a front vowel. This rule operates, in particular, on root vowels followed by suffixes containing a front vowel. The first two columns of the following diagram illustrate schematically what happens in such a configuration.

Next in the diachrony, another phonological process happens which is not related to morphologization: The new front rounded vowels assume what is the default roundedness value for front vowels – viz., unrounded – in several of the Germanic languages in question including English. Thus, instead of /fø:ti/ we get /fe:ti/, and instead of /gø:zi/ we get /ge:zi/. Moreover, there is a vowel change affecting the root vowel of the singular forms. Up to this point, the alternation in the root is just a phonological alternation producing an allomorphy.

Now morphologization consists of three decisive steps. First, as root vowel metaphony is conditioned by the suffix, it is now taken to be conditioned by whatever the function of the suffix is. In the present example, this is plural. In the second step, coding of the grammatical function in question is reanalyzed as discontinuous, viz. root vowel metaphony plus suffix. This is already the beginning of morphologization since what started out as a purely phonological alternation now takes part in a morphological process.

In a last decisive step, the suffixes which originally conditioned the metaphony are lost, in the course of general erosion of suffixal morphology that affects all Germanic languages. Now the only difference between a singular and a plural form on the expression side is between the back vowel in the singular form and the front vowel in the plural form. At this moment, metaphony becomes a new significative structural process in the language whose morphological function is number marking. Speaking generally, the phonology has enriched the significative system. This is the morphologization of a phonological process.

It is quite possible that this is the standard way for an inner modification to come into a language system. It would be good to have more historical cases.

When comparing morphologization to grammaticalization, first a terminological problem must be set aside. The general grammaticalization scale, repeated here from the first lecture, is sometimes completed with a bottom line specifying the processes that lead from one status to the next.

Then the process grammaticalizing a free formative into an affix is called morphologization. And in fact, this is a process transferring something into the morphology just as the morphologization of a phonological alternation as discussed here transfers something into morphology. So in this perspective, the term ‘morphologization’ is polysemous. Here we are concerned with the latter sense.

Morphologization loads a phonological unit or process with meaning. This is semanticization as opposed to desemanticization. Morphologization in the present sense is therefore directly opposed to morphologization as a phase of grammaticalization. Both create morphological items or processes, but introduce them, so to speak, from opposite ends: Grammaticalization introduces them from higher levels of linguistic structure, whereas morphologization introduces them “from below”, viz. from the phonology. Thus, morphologization is a mechanism, beside and distinct from grammaticalization, of enriching grammatical structure.