Alva Noe with great stuff. He explains what he calls the variation effect. Here's one example of it: "At some point in the last four hundred years or so, speakers of languages such as English, German and Danish, but not speakers of French, Italian and Spanish, started to say f whereas earlier we said p....How did this transition from happen? What's remarkable is that the change goes unmentioned in the historical record. How can this be? First, how can people have failed to notice and remark on a steady systematic change in the way people talk?...One hypothesis is that the change was imperceptible because it was gradual. As Deutscher explains, leading linguists as recently as the middle of the last century thought this gradual-change thesis was plausible. But it isn't. It's ludicrous [Fair enough--ES]...The very question — why didn't people notice the sound change when it happened? — relies on the tacit assumption that there was ever a single way people pronounced the words in question. But there is no one way to pronounce these words or any other. The ground of linguistic reality is comprehensible variation. And so there never was a single or unified sound change. Then what happened? All there is and ever was is variation, but what does change, over time, is the frequency of different forms or pronunciations across the field of variations. People didn't change the way they talked. What changed was the number of people who talked one way relative to those who talked another."
Well, okay. But there is a fallacious inference here from a) not preserved in the historical recorded to b) they didn't notice the change. In fact, old people constantly notice (and complain about) the fact that people change the way they talk. (Their complaining is often taken as a sign of aging!) Some newspaper columnists once made a decent living noticing and tracking those changes on the back pages (I always wondered why language columns got put there in the US and in the Netherlands). Moreover, some such changes were directed (as this site notes): http://books.google.nl/books!