One of the primary areas of change within a language is the change in its system of sounds. These changes can be divided into two class: conditioned changes, where vowels and consonants are affected by neighboring sounds to produce a change in how they are produced, and unconditioned changes, where the sounds change regardless of their phonetic environment.

Principle of Least Effort

The principle of least effort, also called ease of articulation, describes how speakers of a language naturally seek to expend the least effort possible to articulate sounds without losing intelligibility. For consonants, the most common change of this type is assimilation, where the consonant changes how it is produced to be more similar to a neighboring sound. We have three types of assimilation:

• assimilation of place, where a consonant changes its place of articulation
• assimilation of manner, where a consonant changes its manner of articulation
• assimilation of voicing, where a consonant changes whether or not it is voiced.

Assimilation of Place

Assimilation of place is very common in English, especially with the three nasal phonemes. For example, take the phoneme [n] in the word “pan.” It is a voiced alveolar nasal. But in the word “pancake” the [n] often becomes the velar nasal, that is [ŋ], because it has assimilated to the following velar sound of the [k] in cake: [pæŋkek]. The same assimilation of place with [n] becoming [ŋ] in words like “incredible,” or “ink.”

Another nasal assimilation of place occurs in words like “symphony,” where the bilabial [m] is followed by a labiodental fricative [f]. What is actually pronounced here is a labiodental nasal, represented by the symbol [ɱ], so that it is pronounced [sɪɱfəni].

Another very common type of assimilation of place is called palatalization, which means that sounds are moved towards the palate. Palatalization occurred in the early Modern English period when the vowel /u/ in some words developed a semivowel glide before it, the palatal sound /j/. When this palatal sound /j/ came after the alveolar sounds /s/, /z/, /t/, /d/, it pulled them back towards the palate, creating the following new pronunciations (in linguistics, the symbol > means “becomes,” as if it were an arrow, pointing to the new creation). Think of the following words:

• [sj] > [ʃ] sure, sugar
• [zj] > [ʒ] pleasure, measure
• [tj] > [tʃ] nature, creature
• [dj] > [dʒ] educate, adulate

The spelling of these words, which was established before the phonological change, gives away how these words would have been pronounced in Shakespeare’s day: “sure” and “sugar” were pronounced with [s], “pleasure” and “measure” were pronounced with [z], and “nature” and “creature” were pronounced with a [t]. Furthermore, the “u” was pronounced [u], not [ju]. But after the [u] developed a [j] glide before it, the new pronunciations developed. (Note that the [j] glide did not develop before [u] for all speakers, and there are still speakers of English who pronounce words like “pleasure” with a [z] and have no [j] before the [u]. In American English there is a divide between people who pronounce words like “news” or “tune” with a straight [u] and those who pronounce them with [ju]).

If we concentrate on Present-Day English, we see the effects of palatalization ongoing, not only within individual words like discussed above, but in word boundaries. For example, when the word like “don’t,” which ends with an alveolar [t]. is followed by a word that begins with [j], as in the phrase “don’t you,” then in some dialects the [t] is palatalized in the same way as above to become [tʃ]. This also happens between words with [s] and [d]:

• [sj] > [ʃ] “Bless you” pronounced [blɛʃ ju] (“Blesh you”)
• [tj] > [tʃ] “Don’t you” pronounced [dontʃ ju] (“Donchu”)
• [dj] > [dʒ] “Did you” pronounced [dɪdʒ ju] (“Didge you”)

Assimilation of Manner

In addition to allophones changing their place of articulation through assimilation, some change their manner of articulation. This is a much rarer type of assimilation, but it does occur. For example, for some speakers the dental stops in phrases like the following may become fricatives to match the fricatives that follow them:,/p>

• “read this”: [rid ðɪs] > [rið ðɪs]
• “that thing”: [ðæt θɪŋ] > [ðæθ θɪŋ]

Assimilation of Voice

In this type of assimilation, a voiceless sound that is near a voiced sound will become voiced, or a voiced sound that is near a voiceless sound becomes voiceless. This type of assimilation is incredibly common in English. For example, the plural ending –s can take the form [s] or [z] depending on the voicing of consonant it follows. If the noun ends in a voiceless consonant like “book,” then the plural will also be a voiceless [s], but if the noun ends in a voiced consonant as in “dog,” then the plural will be formed with the voiced [z].

The same process occurs with the past tense ending –ed. In this case, the original ending is voiced [d]. It remains voiced in words that end with a voiced consonant, like “joined” [dʒɔɪnd], but in words that end with a voiceless sound, it assimilated to the voiceless [t], as in “jumped” [dʒʌmpt].

Other types of sound changes

Simplification

Another product of the principle of least effort is simplification. This change does not involve a change in features but rather the loss of a segment when consonants occur in groups of two or more. Take the word “hand,” pronounced [hænd]. If we make it plural, the word ends in three consonants, “hands,” which is usually pronounced with a reduction of that cluster to only two consonants [hændz] > [hænz].

It is not uncommon that consonants will be simplified even in groups of two. For example, there are English speakers who pronounce the word “hand” without the final [d] even in the singular. This is more common in words that receive little stress within a sentence, such as “and,” which is regularly pronounced without the final [d].

Metathesis

Metathesis is the reversal of two sounds. Common ones today usually involve the phoneme /r/. For example, in the word “iron,” the spelling reveals that the word used to be pronounced with the [ɹ] before the vowel, while now we pronounce it after the vowel. The same is true of the word “third,” where the word “three” shows the original order of the [ɹ] and the vowel. These two examples are accepted as standard pronunciations, but there are non-standard examples as well, such as “purty” for “pretty.”

Examples of metathesis with sounds other than [ɹ ] are more rare today, but one that remains common is “aks” for “ask.” The form “aks” was the more common form in the Old and Middle English periods, used by both King Alfred and Chaucer. It can still be found in non-standard dialects throughout the U.S. and England.