The lexicon is full of elements which were once entirely functional morphemes but which for various reasons – most often the destructive effects of sound change – have become defective and eventually useless. They still get replicated and passed on from generation to generation simply because we acquire our mother tongue (or learn a foreign language) whole, without testing the functionality of every little detail and without repairing those that might seem to have been broken. Linguistic communication involves a lot of redundancy, so a small local loss is easy to tolerate: other elements will take over the function of the damaged one.
For example, the suffix -th, forming deadjectival nouns in early English, is now practically dead. We are still able to detect its presence in words like length, strength, warmth, breadth, width, etc., but the process that formed these words (in a very distant past) is no longer productive, as opposed, for example, to the formation of nouns in -ness. We can say awsomeness, weirdness, and coolness (and interpret such words correctly even in the unlikely case that we have encountered them for the first time), but not “awsometh”, “weirdth”, or “coolth”. We do not understand today why the vowel od length and strength should be /e/ (rather than /ɒ/, as in long and strong), why we say /wɪdθ/ rather than /waɪdθ/, or why, on the other hand, there is no need to modify the vowel of warm to get warmth. Is youth related to young? The spelling is similar and suggestive of a relationship, but how exactly they might be related is a mystery (unless you happen to be a linguistic expert paid for knowing such things).
In Old English the suffix was still quite productive. Also the process of i-umlaut, responsible for the fronting of the vowel of length, strength, and breadth, had not yet degenerated into an obscure fossil remain but was still utilised to some extent as a morphological device. Consider OE fūl ‘dirty, polluted’. The suffix -þ, when added to it, caused the vowel to become front (though still pronounced with rounded lips, like German ü or French u): the OE spelling was fȳlþ (phonetically /fyːlθ/). Whence the fronting? If you look at the corresponding Old High German noun, fūlida, the reason becomes clear: the suffix once contained an *i, lost in the pre-literary history of English, but not before it had exerted its assimilatory effect on the preceding syllable. In Old English, the addition of the suffix and the accompanying vowel change functioned together as a complex marker indicating a noun derived from an adjective (note the redundancy of such double marking, given up in the case of warmth).
What happened later? Long /yː/ was regularly shortened when it was followed by a consonant cluster (this is also the reason why we have short vowels in depth, breadth and width), and by the end of Middle English the resulting /y/ had become unrounded, merging with short /i/. The modern outcome is filth /fɪlθ/. Meanwhile, the long vowel of fūl developed regularly, becoming a diphthong in the fifteenth century as a result of the Great Vowel Shift. The outcome is ModE foul /faʊl/. Both words are short, and whatever similarity has remained between them hardly compels one to believe that they must be related. In fact, any fully competent speaker of Modern English asked to form a noun from foul will likely suggest foulness – partly because filth, liberated from its original obligations, has shifted its meaning from simply ‘dirtiness’ to ‘disgusting stuff’. We no longer break a word like filth into meaningful smaller parts. Filth is now unanalysable, and the final -th is not recognised for what it used to be. It has become junk.
|Some of it will be recycled|
Junk morphology may be compared to “junk DNA” – the sequences in the genome that have lost their original “meaning”. The genome is littered with the slowly decaying débris of once-functional sequences: former genes (now pseudogenes) damaged by a mutation that has rendered them incapable of coding for a protein, retroviruses that have been infecting the ancestors of modern organisms over tens of millions of years, and after integrating their code with the host’s DNA lost their ability to break free and go on infecting new cells... and all that junk. It survives because it accumulates faster than purifying selection is able to take effect. In other words, junk is relatively harmless, so it is not worthwhile to remove it quickly. It can even find a use again: occasionally a broken sequence can be co-opted in a novel function. As we shall see, the same is true of junk morphology. But this is something to be continued in future posts.