Assimilation is a natural process which happens in every language: one phoneme is turned into another because of the influence of a neighbouring sound. So, this stands at the very centre of connected speech.
The most common type of assimilation is regressive, that is, it operates backwards: the phoneme undergoing the change is influenced by the sound that comes after it. For example, the phrase that man [ ðæt ˈmæn] might be pronounced [ ðæp ˈmæn] because, since /m/ is a bilabial , the plosive alveolar /t/, which is placed immediately before it, becomes a bilabial as well (the also plosive /p/).
One crucial thing is that assimilation is mainly carried out unconsciously, so speakers don’t normally realize what they are doing and tend to be surprised -even indignant- when told that the actual sounds they produce don’t always match the spelling.
But why, you may well ask, does assimilation happen at all? The reason is quite simple: our articulators (tongue, lips, teeth, etc.) have to move from one position to another -from /n/ to /b/, for example-, but certain changes are difficult to make in the required time, so they take a shortcut.
Let’s see this case in detail, as an example:
One boat Un barco
Changing from alveolar /n/ to bilabial /b/ is not easy because it involves too much movement in the mouth. It can only be done accurately in slow, careful speech. If we are speaking rapidly we turn the alveolar nasal /n/ into a bilabial nasal /m/, so that we are already prepared for the bilabial /b/. In short, we skip one step (alveolar) and go directly to the next one (bilabial). That’s why we normally say:
ǀ wʌm ˈbəʊt ǀ ǀ um ˈbarko ǀ
And that’s also why, in Spanish, the prefix en becomes em when it’s followed by bilabials p and b (empaquetar, embotellar). As you see, it’s a completely natural process.
There is also a progressive assimilation, in which a phoneme is changed because of the influence of a preceding sound: open /ˈəʊpən/ and ribbon /ˈrɪbən/ can be pronounced /ˈəʊpm/ and /ˈrɪbm/ (the /ə/ is dropped and the bilabials /p/ and /b/ turn the /n/ (alveolar) into the bilabial /m/. Notwithstanding its inclusion in academic books and treaties, the importance of progressive assimilation is really marginal to the interests of the English speaker, so we’ll disregard it and concentrate on the first type.
And now comes a crucial question:
Is assimilation obligatory? No it isn’t. But it’s natural and it makes the speaker sound more fluent. One important point is that it doesn’t have to be done all the time, that is, on every single occasion. But, by the same token, a speech totally deprived of assimilation sounds very artificial, even stilted.
Listen to this interesting recording:
This is now going to be a struggle between the good guys and the bad guys. Now the army, he says, the army top brass are the bad guys, the small number of intellectuals who are campaigning to reopen the trial are the good guys (Robert Gildea, BBC4).
The speaker doesn’t assimilate the phoneme /d/ to a /g/ in the phrase good guys, but he does do it in bad guys. So he says
ǀ gʊd gaɪz ǀ but
ǀ bæg gaɪz ǀ
Why does he choose to do it so? This is probably a matter of personal taste or habit, or it might depend on the moment, the pace of the speech or other factors. Actually, it doesn’t matter. Some speakers consistently assimilate certain sounds and not others, and the same can be said about some expressions or combinations of words. The fact that someone pronounces should go as ǀ ʃʊg ˈgəʊ ǀ doesn’t mean that he or she assimilates every /d/ to a /g/ when it’s followed by a velar. What is certainly true is that assimilation is extremely common in the speech of native speakers and that it makes non-native speakers sound more natural as well.
In the following articles, we are going to study different cases of assimilation. On the face of it, the prospect might seem daunting, but once you get started you’ll realize that actually it’s quite easy. What you’ll probably feel is a sense of relief. Assimilation is a very natural phenomenon, so you’ll speak more freely and comfortably knowing that those changes are perfectly correct and even expected. You’ll also understand native speakers better.
Three points to remember
The cases we are going to study have a number of common features. Keep the following three points in mind (it would be useful to have this table at hand):
- Alveolar. All the sounds subject to variation here are alveolar: /t/, /d/, /n/, /s/ and /z/. Alveolar consonants are especially unstable in English.
- Place of articulation. In the majority of cases, the only change these sounds undergo is one of place of articulation. E.g., /t/ (alveolar) can become either /p/ (bilabial) or /k/ (velar). The manner of articulation remains the same (plosive or fricative) or changes very little (from plosive to affricate).
- Voicing. Crucially, the voicing remains unchanged. Voiceless /t/ can turn into voiceless /p/ and /k/. Voiced /d/ can become voiced /b/ and /g/. There is only one case in which there is a change of voicing (from /z/ to /ʃ/). If you keep in mind this point, you’ll find these processes much easier to learn.