Typical sound change processes.

A. Assimilation. Many of these changes seem to us to be “sloppy” speaking. For example, in early Latin, the word for impossible is inpossibilis, but in later Latin, the word was impossibilis. The n changed to an m because the m sound is closer to a p than n. This process is called assimilation. Over time, laziness created a new word—the one we borrowed from Latin that is so proper to us today!

in-possibilis > im-possibilis

B. Consonant weakening. Similarly, over time, consonants tend to weaken and even disappear.

1. In Latin, the word for ripe was maturus. In Old Spanish, the word was pronounced the way it is written today: maduro; the t weakened into a d, and the s at the end vanished. But in Castillian Spanish today, the word is actually pronounced “mathuro,” with the soft kind of th in mother. In Old French, the word was similar, pronounced “mathur,” but since then, the th sound has dropped out completely, and the word is just mûr.

2. This is not “exotic”; it is typical of English, as well. Notice that in the word bottle, we do not say “BAH-tull”—we say something like “bahddle.” This is because the t has weakened to a d-like sound over time.

C. Vowel weakening. Vowels are fragile as well. The reason name is spelled with an e at the end is because the spelling corresponds to an earlier stage in our language. Once, the word was “NAH-meh.” Over time, the e weakened to an “uh” sound: “NAH-muh.” Finally, the e withered away completely.

D. Sound shift. A question here might be why languages do not simply wear away into dust if this is all that sound change is about. In fact, sounds often just transform into new ones.

The Great Vowel Shift. For example, I oversimplified in describing the evolution of the word name. The first vowel changed as well: we do not say “nahm” but “naym.”

1. Vowels in the mouth. This is because starting in the late 1300s, many English vowels began to shift to new ones. Much of our spelling reflects the stage before this shift. To understand it, we need to see how sounds fit into the human mouth. These are the basic vowels the way we learn them in, for example, Spanish:

2. How the Great Vowel Shift happened. Vowels began shifting upwards on this grid.

Notice that a word such as FOOD is spelled with two o’s. It used to be pronounced “fode,” but its pronunciation moved up into the “u” region and became what it is now. The spelling has stayed the same, but the language has moved on. Over on the other side of the chart, a word like FEED was originally pronounced “fade,” but the sound moved upward so that now it is pronounced with the “i” sound.

While words such as FEED left their “slots,” words with the ah sound of “NAH-muh” moved up and took their place. This is why the word is now pronounced “naym”—and why made is pronounced the way it is instead of the way it is spelled, “MAH-duh,” and so on.

3. The process continues. Many Americans today pronounce what is written as aw as ah, as in “rah fish” instead of “raw fish.”

4. Similar shifts elsewhere. When the erosion of consonants and the shifting of vowels combine, words can transform so far that we would never perceive any relationship between stage one and stage two without documents showing us the shift through the ages. In Latin, water was aqua. In Spanish, the consonant softens to a g: agua. But in French, the consonant has vanished, and the vowels have changed and combined into one, so that the word is eau, pronounced just “oh.”