What are the most common sound changes in natlangs?

Question

What sound changes are most common in natural languages, and in what order do they usually occur? Are there any factors to take into account when modelling sound changes for a conlang that is supposed to resemble a natlang?

Answer 1

By far the most common changes are assimilation, one sound becoming more similar to a nearby sound, and lenition, a sound shifting to require less articulatory effort. These are both broad categories that encompass a lot of more specific types of changes.

Assimilation can include:

• A sound taking on an adjacent sound's features, like md > nd or zt > st
• A cluster turning into a single sound, like ts > ss (total assimilation)
• A sound becoming voiced between vowels (which are usually voiced), or voiceless at the edge of a word (next to the voiceless silence)
• A vowel taking on the features of vowels in other syllables, like uti > yti (vowel harmony)
• And various others!

Lenition can include:

• Sounds using less of a closure, like k > x or x > h
• Sounds disappearing entirely, like h > ∅ (deletion)
• Vowels moving toward the center of the vowel space, like a > ə (laxing)
• Long sounds being pronounced for less time, like tt > t (shortening)
• Multiply-articulated sounds losing one of their articulations, like kw > k (or p)
• And more!

Since these both reduce the amount of articulatory effort needed, they're very common types of changes. But they also generally involve losing information, so other types of changes will work to counteract this over time (for example, morphological changes to restore some of this information).

Answer 2

Things are probably hard to quantify, but some specific sound changes seem to be more frequent than others, most notably:

/h/ -> /∅/ (loss of /h/)

The consonant system often has gaps at /p/ and /g/:

/p/ -> any: is mostly /p/ -> /f/ or /p/ -> /ɸ/, can go further via /h/ to nothing /∅/

/g/ -> any: lots of choices, e.g., /g/ -> /ʤ/, /g/ -> /k/, /g/ -> /ɣ/ (and further to nothing /∅/)

Answer 3

Here are a couple sound changes I use when I'm not sure what to do:

• Voiceless consonants becoming voiced between two vowels (intervocalic voicing)
• [u] and [o] becoming [y] and [ø] in the environment _Ci (that is, when the next vowel is [i])
• Voiceless nonsibilant fricatives becoming [h]
• [h], [x], [ħ], or other weak consonants being lost and lengthening the previous vowel (compensatory lengthening)
• Clusters of two voiceless stops becoming geminated forms of the second one (this is sometimes called Italian-style gemination)
• Weakening voiced stops to liquids (e.g. [b] to [w])