gestaltist wrote:People are lazy creatures and they don’t tend to complicate their lives if they don’t have to. Given the prevalence of simple vowel systems like /a e i o u/ what was the advantage of complicating the system?
Exactly that laziness, as I explained above. Simple inventories create allophony, allophony may lead to new phonemes. Note that it's not always predictable whether this happens: Spanish has afaik an extremely stable /a e i u o/ inventory, while closely related Portuguese has added all kinds of weirdness. Also note that there's no "advantage of complicating the system", as people do not deliberately add complexity. It just happens as the result of sound change.
jal wrote:Also note that there's no "advantage of complicating the system", as people do not deliberately add complexity. It just happens as the result of sound change.
I'll second this. It's not that language changes specifically to be less complex, though after a point it becomes so complex that leveling the system happens (the ri-DIC-ulous morphological complexity of Old Irish that collapsed into a much more sane system, for a well-known example). There's always tradeoffs. In the case of Germanic, the combination of strong initial stress and reassigning unstressed vowel features to stressed vowels (umlaut) allowed for extensive syllable-dropping, but I don't think it would be accurate to say that feature reassignment was done in order to to make the system less complex in another way. Rather there was redundancy that was eliminated, though not without its own problems (irregular plurals, regular morphological causation into sporadic lexical (in)transitive-causative pairs, and move towards fixed word orders).
