Introduction

We have seen elsewhere (speech) that (articulatory) phonetics is the subcategory of speech that studies articulation, i.e. how the sounds of particular languages are articulated in particular contexts. [The other subcategory is phonology.] This article is restricted to a discussion of consonant sounds, for two reasons. First, vowel sounds are complex, and consequently difficult to describe. Second, in the majority of articulation disorders it is the consonants that are most disrupted, and so a focus on consonants can better help our understanding of speech disorders.

Consonants

Consonants are closed sounds. This means that there is some type of obstruction to the airflow from the lungs by parts of the mouth coming into contact with each other, or very nearly contacting, thus closing off the free flow of air. For example, the lips could come together for the sound ‘b’ as in the word ball, or the tongue tip could almost contact the gum ridge (alveolar ridge) just behind the upper incisors for the sound ‘s’ as in sun. These contacts, and near contacts, impede the free flow of air through the vocal apparatus¹. It is this kind of closure that characterizes consonant sounds. In English there are approximately 24 consonants and these are arranged into five main groups: (1) plosives, (2) nasals, (3) fricatives, (4) affricates, and (5) approximants. We will now consider each of these in turn.

Plosives

Plosive consonants are oral sounds, i.e. the soft palate is raised so that air from the lungs cannot pass upwards into the nasal cavity. The air can only, therefore, escape through the oral cavity. All plosives are produced by a complete obstruction of the airflow at some position in the mouth, for example by the lips coming together. Air from the lungs is then compressed behind the temporary obstruction and the air pressure builds up in the mouth. The obstruction is then removed (in this case, by the lips parting) and the air rushes out of the mouth with a slight ‘explosion’, hence the name ‘plosive’.

Plosives occur in pairs and may be produced with or without the vocal folds (vocal cords) vibrating. Sounds produced with vocal fold vibration are said to be voiced, whereas those produced without vocal fold vibration are voiceless. There are three pairs of voicelessvoiced plosives:

bilabial plosives

These are produced with the two lips coming together to form a complete closure and they are, therefore, known as bilabials, i.e. two lips. They are:

‘p’ as in pit and cop

‘b’ as in bit, and lab

The developing child usually consolidates the use of bilabial plosives between 1;06-2;00 years of age.

alveolar plosives

The second pair of voicelessvoiced plosives is articulated with the tip of the tongue contacting the alveolar ridge just behind the upper incisors. They are:

‘t’ as in tin and hat

‘d’ as in din and had

Again, by placing your fingers on your larynx as you articulate these sounds, you should be able to determine that ‘t’ is voiceless whereas ‘d’ is voiced.

The developing child is usually expected to have consolidated the use of alveolar plosives between 1;06-2;00 years of age.

velar plosives

The third pair of plosive sounds is made with the back of the tongue contacting the soft palate or velum. They are:

‘k’ as in coat and lock

‘g’ as in goat and log

The velar plosives take a little longer for the developing child to acquire, typically emerging between 2;00-2;06 years but they may not be fully consolidated until 2;06-3;00 years of age.

Nasals

Nasal sounds are similar to plosives in that there is a complete obstruction of the airflow in the mouth but, in contrast, the air pressure is not allowed to build up behind the obstruction. Rather, it is allowed to escape through the nasal cavity by lowering the soft palate. Consequently, unlike plosives, it is possible to take a breath and prolong a nasal sound.

There are only three English nasal consonants and they are all voiced. They are made in exactly the same position in the mouth as the plosives and, therefore, they are named similarly:

bilabial nasal ‘m’ as in mop and ham

alveolar nasal ‘n’ as in not and loan

velar nasal ‘ng’ as in wing and ring

For the developing child, both the bilabial nasal ‘m’ and the alveolar nasal ‘n’ are typically consolidated between 1;06-2;00 years of age. The velar nasal ‘ng’, however, emerges a little later – appearing between 2;00-2;06 years but may it not be fully consolidated until 2;06-3;00 years.

Fricatives

These are formed by a narrowing of the oral cavity by two articulators, such as the lips, teeth, tongue or palate, coming into near contact. The air forcing its way through the narrow gap creates turbulence or friction, hence the name fricative.

Like plosives, fricatives mainly occur in voicelessvoiced pairs. There are four of these:

labio-dental fricatives

These are articulated with the near contact of the bottom lip and the upper incisors. They are:

‘f’ as in fan and half (voiceless)

‘v’ as in van and rave (voiced)

The voiceless labio-dental fricative usually emerges before the voiced labio-dental fricative, with ‘f’ emerging between 3;00-3;06 years and ‘v’ emerging between 3;06-4;06 years.

dental fricatives

These are made by the tongue tip nearly contacting the back of the upper incisors. The tongue is relatively flat and a narrow slit is formed in the mouth. The friction is created as the air passes over the tongue and past the upper incisors. They are:

‘th’ as in thin and hearth (voiceless)

‘th’ as in that and loathe (voiced)

These are late-emerging which are typically not consolidated until at least around 4;06 years of age.

alveolar fricatives

These are formed by the front of the tongue nearly contacting the alveolar ridge. They are:

‘s’ as in sun and house (voiceless)

‘z’ as in zoo and raise (voiced)

There is controversy over when ‘s’ is consolidated. Some argue that this happens as early as 3;00-3;06 years. However, there appears to be a wide variation in the acquisition of this sound and some children still may not have fully consolidated the sound by 4;06 years. The voiced counterpart ‘z’ is generally recognized to emerge later than the voiceless sound, becoming consolidated between 3;06-4;06 years.

post-alveolar fricatives

These are made further back in the mouth, with the middle of the tongue coming into near contact with the palate just behind the alveolar ridge. They are:

‘sh’ as in shop and bash (voiceless)

‘zh’ as measure and beige (voiced)

The voiceless post-alveolar fricative ‘sh’ emerges anytime between 3;06-4;06 years and the voiced post-alveolar fricative ‘zh’ is usually not consolidated until the child is almost 4;06 years of age.

glottal fricative

There is one more fricative sound in English which is distinguished on the basis that it is the only fricative that does not pair with another sound. It is made deep down in the throat by allowing air to escape through the gap between the vocal folds (the glottis):

‘h’ as in house and who (voiceless)

The glottal fricative is typically the first fricative to emerge and it can usually be identified in the speech of children between 2;00-2;06 years.

Affricates

All of the consonant sounds described so far are produced with either a complete obstruction of the airflow or a narrowing of the mouth passage. Affricates are, however, produced by a combination of these two methods. They begin with a complete obstruction formed by the tongue tip contacting the alveolar ridge, like alveolar plosives. Then the air, instead of being released out of the mouth suddenly with an ‘explosion’, is released slowly with friction behind the alveolar ridge as the tongue moves backwards towards the palate. Consequently, they are known as post-alveolar affricates. They are:

‘ch’ as in chore and hatch (voiceless)

‘j’ as in jaw and large (voiced)

Both ‘ch’ and ‘j’ typically emerge between 3;06-4;06 years.

Approximants

Approximants are consonants which are produced without either complete closure (e.g. as in plosives and nasals) or near closure (e.g. as in fricatives). Rather, they are produced in such a way that two articulators approximate closely but not such that friction is created. They are four of these and they are all voiced:

bilabial approximant ‘w’ as in win and we

alveolar approximants ‘r’ as in red and run and ‘l’ as in lay and hall

palatal approximant ‘y’ as in yes and yell

The first approximant to develop is ‘w’ (1;06-2;00 years). The second is ‘y’ (3;00-3;06 years) and the third is ‘l’ (3;00-4;06 years). There is, however, considerable variation in the acquisition the final approximant ‘r’, being anything from 4;00 years up to 6;00 years in some instances.

Summary of English consonants

If we were to list all the speech sounds in a particular language that a person is capable of articulating this constitutes their phonetic inventory. Table 1 summarizes all 24 of the English consonant sounds in relation to their manner of articulation (i.e. whether they are a plosive, nasal, fricative, affricate or approximant) and their place of articulation (i.e. bilabial, labio-dental, dental, alveolar, post-alveolar, palatal, velar, glottal).

Table 1. English Consonants