We’ve written about several big, historic sound changes, like umlaut and Grimm’s Law. But why does pronunciation have to change at all? Why can’t it just stay the same forever? Surely, that would be easier for everyone (especially us historical linguists trying to reconstruct speech from a time before sound recording).
Without diving in too deep today, let’s look at two of the big forces playing tug-o’-war with our phonemes (and the rest of our language): good, old-fashioned laziness and the need to be understood.
I called the first force laziness, but perhaps a kinder appellation would be “conservation of energy.” Unless you live by yourself in a cottage deep in some leafy forest somewhere, you probably regularly do a fair amount of communication (yes, even you introverts). Speech1 is a repetitive motion, and like other repetitive motions (e.g. signing your name), we unconsciously streamline it as it sinks deeper and deeper into our muscle memory. ‘Cannot’ in most instances becomes ‘can’t’; the <tt> in ‘button’ becomes [ʔ] instead of [t].2
This tendency to expend the least amount of effort in language production is called ease of articulation. This is what leads to phenomena like umlaut: it’s easier to pronounce consecutive vowels in the same area of the mouth, so back vowels are pulled forward after front vowels (e.g. Proto-Germanic *mūsiz “mice” becomes OE *mȳs). Similarly, vowels in unstressed syllables tend to relax into schwa. Why enunciate every sound when you don’t really have to? (Except sometimes you do have to.)
Ease of articulation is one thing, but on the other hand, language can’t allow itself to devolve into a mushy, mumbly mess. That would be self-defeating. When your whole purpose in life is to communicate messages, by gum! you’ve got to make sure you can effectively communicate a message. If things become too similar, a language finds ways to self correct, to dissimilate. Dissimilation is a process whereby two linguistic elements that are confusingly alike are pulled back apart to a reasonable, comprehensible distance. Take, for example, the OE pronouns hē “he” and hēo “she”. Linguists aren’t exactly sure which specific sound change stepped in to shift hēo to she, but I think we can all agree that it’s easier to tell who’s who with more distinct pronouns. Or in another case, we find the word pilgrim ultimately comes from Latin peregrinus “foreigner, traveler”. In Latin words with far too many /r/s, one of them commonly became an /l/ over time to unmuddy the waters.
Though they seem almost like an uptight, mothering older sister (dissimilation) and her carefree, lackadaisical little brother (ease of articulation), these two processes work in tandem as much as they work against each other. You could almost say they bring balance to the Force. (But you could also say that languages are wild, organic things that refuse to be tied down. It’s not you, it’s them. And as you may have guessed, ease of articulation and dissimilation aren’t the only suspects complicating this situation. We’ll get there.)
1 It’s something we haven’t brought to the forefront in a while, but I’d like to remind you that when we talk about “speech,” we could just as well be talking about signing. Sign languages function much like spoken languages.
2 Depending on your dialect.