Phonology is the study of the rule system that governs how particular speech sounds are used to produce meaningful words. It investigates the systematic organization of sounds in a particular language. In particular, phonology is concerned with phonemes. These are speech sounds that are capable of creating a distinction in meaning between different words. If two speech sounds can contrast to make a distinction in meaning then they are said to be phonemes. For example, the words tin and din form what is known as a minimal pair. This means that they differ in only one element, in this case either the initial consonant ‘t’ or ‘d’. We see that ‘t’ and ‘d’ are, therefore, capable of contrasting different meanings and so they are considered to be phonemes. In English there are around 24 consonant speech sounds that are capable of displaying this contrastive function, i.e. there are around 24 consonant phonemes.

Vowels can also function phonemically. However, this article focuses solely on consonants.

Phonological processes

Children below the age of about 4;06 years may not have sufficient ability to fully co-ordinate the movement of their vocal apparatus. As a consequence, certain sounds, sound combinations or transitions from one sound to another may be currently too difficult. The child may, therefore, simplify the production of complex words. However, in the typically developing child, these simplifications are not random but fairly predictable.

Many so-called phonological simplifying processes have been identified. In fact, there are far too many to cover adequately in this article. However, I will provide some selected examples that will serve to illustrate how phonological processes operate. We will consider two broad categories: (1) structural simplifications, and (2) systemic simplifications.

Structural simplifications

Structural simplifications involve some alteration to the structure of a particular word. We will consider three:

  1. reduplication

  2. deletion

  3. cluster reduction


Reduplication occurs whenever the initial CV syllable in a multisyllabic word is repeated.

[See On the Definition of ‘Reduplication for further comments on the above.]

Consider the word bottle said as bobo.

In this example, the first syllable is reduplicated. This is a fairly simple structural process that can be summarized as:

syllable1 syllable2 syllable1 syllable1

Other examples include biscuit being said as bibi, and water being said as wawa.


A simple way to alter the structure of a word is to omit particular speech segments. There are two main speech segments that are typically deleted: (1) consonants, and (2) weak syllables.

consonant deletion

Consonant deletion occurs whenever a consonant in syllable-initial or syllable-final position is omitted.

Children may delete sounds at the beginning of words (initial consonant deletion), e.g. cat becomes at, boat becomes oat or at the ends of words (final consonant deletion), e.g. lid becomes li, cup becomes cu.

Consonant deletion is a typical phonological process for children between the ages of 2;00-3;06 years.

weak syllable deletion

Weak syllable deletion occurs whenever the unstressed or weak syllable of a multi-syllabic word is omitted.

In this process whole syllables are deleted. These are typically unstressed syllables (e.g. the ‘ba’ in banana; the ‘to’ in octopus). So, for example, banana may become nana; octopus may become ocpus.

This is a typical process In children between the ages of 2;00-4;00 years.


Metathesis occurs when two consonants within a syllable are placed in a different order.

In sum, there is a reordering of the sequence of consonants (C) and vowels (V) within a syllable. For example, in a CVC sequence the first and last consonants may be reversed, e.g. cup becomes puc; dog becomes god.

Cluster reduction

Cluster reduction occurs when one or more consonants in a cluster is omitted.

We know that some words in English are structured with clusters of more than one consonant in a sequence, e.g. plan (CCVC), mast (CVCC).

These clusters may be deleted completely, e.g. plan (CCVC) becomes an (VC); mast (CVCC) becomes ma (CV).

Alternatively the cluster may be partially reduced by only articulating one of the consonants in the cluster, e.g. plan (CCVC) may become pan (CVC) or lan (CVC); mast (CVCC) may become mas (CVC) or mat (CVC).

Cluster reduction is often observed in children between 2;00-3;06 years of age.

Systemic simplifications

These phonological processes systematically vary a particular type of speech sound and replace it with another speech sound. We will discuss the two main categories:

  1. substitutions

  2. assimilations


Again, there are many different types of substitutions that can be made in typically developing speech. We will look at just three of these to get a flavor of how these phonological processes operate.


Fronting occurs when any consonant that is made posterior to the alveolar ridge is substituted by another consonant that is made at or in front of the alveolar ridge.

For example, goat may be said as doat. Here the back sound ‘g’ (usually made with the back of the tongue lifting towards the back of the mouth) is substituted with the front sound ‘d’ (made towards the front of the mouth, with the tongue tip lifting towards the gum ridge just behind the upper incisors). Other examples include cod being said as tod, and gun being said as dun.

Fronting is often widespread in children from the age of 2;00 years up to as old as 4;06 years.


Backing occurs whenever a non-velar or non-glottal consonant (i.e. a bilabial, labio-dental, dental, alveolar, post-alveolar or palatal consonant) is substituted by a velar /k ɡ ŋ/ or glottal /h ʔ/consonant.

For example, bun may be said as gun. Here the front sound ‘b’ (usually made with the two lips coming together) is substituted with the back sound ‘g’ (made with the back of the tongue lifting towards the back of the mouth). Other examples include door being said as goor, and tar being said as car.

Backing is frequently observed as a typical process in children from 2;00-3;00 years of age.


Stopping occurs when continuant consonants (nasals, fricatives, affricates and approximants) are substituted with a stop consonant /p b t d k g ʔ/.

For example, consider the word sock. The initial ‘s’ sound is sustainable, i.e. you are able to prolong this sound when you say it. Try it now by taking a deep breath and see how long you can say the single sound ‘ssss…’ It is evident that you can hold this sound for several seconds. But now try and sustain the sound ‘t’ (as in the words tip and hot). You’ll see that this sound cannot be sustained – you say the sound and then it is over in a moment. This is an example of a plosive sound (see Consonants).

Now, suppose the word sock is said as tock. The sustainability of the initial ‘s’ has been stopped by substituting it with the unsustainable sound ‘t’. This is, therefore, known as stopping. Other examples include van said as ban, and ship said as dip.

Depending on which sustainable speech sound is stopped, this process appears in the speech of typically developing children from 2;00-4;06 years of age.


Assimilation occurs when one speech segment is transformed into another owing to the influence of a neighbouring segment.

A relatively common assimilation in children up to about the age of 3;00 years is word-final de-voicing.

word-final de-voicing

To understand this process we need to be clear about the distinction between a voiced consonant and a voiceless consonant. Simply, a voiced consonant is one which is made with the vocal folds (vocal cords) vibrating (e.g. ‘b’, ‘d’, ‘g’, ‘z’, ‘v’) and a voiceless consonant without vibration (e.g. ‘p’, ‘t’, ‘k’, ‘f’, ‘s’). It is relatively easy to determine which is which by simply placing your fingers on your voice box (larynx) whilst you say the sound. If the sound is voiced you will feel the vibrations caused by the moving vocal folds in your fingers. Of course, if it is voiceless you will not feel any vibrations.

Now, children between the ages of 2;00-3;00 years of age seem to find the production of voiceless consonants simpler than the production of voiced consonants when they occur at the ends of words. So, the word bed may be said as bet. Here the word-final voiced consonant ‘d’ is assimilated into its voiceless counterpart ‘t’. Other examples include bag being said as bak, and lab being said as lap.

Co-occurrence of phonological processes

The phonological simplifying processes described here should serve to illustrate that most of the errors children make are not really errors at all. In fact, the majority of children are still using some phonological simplifying processes up to the age of 5;00 years, and some even beyond this.

As with most processes of human communication, phonological simplifying processes do not always operate in isolation from other processes, or from different presentations of the same process. For example, the process of stopping does not have to operate exclusively in either initial position (e.g. foot being said as toot) or final position (e.g. bash being said as bat): it may operate in both positions at the same time. For example, in the word sash, if both the initial and final sustainable consonants are stopped, this could render the words as tat. Other examples of stopping both initial and final sustainable consonants in the same word include thief being said as tiet, and sauce being said as taut.

It is also possible to have several processes affecting speech production at any one time. Consider the following words which provide examples of two or more co-occurring processes.

stack being said as tat

This involves two processes:

  • initial cluster reduction of ‘st-’ to ‘t-’

  • fronting of the final back sound ‘k’ to the front sound ‘t’

splash being said as ap

This also involves two processes:

  • deletion of the initial cluster ‘spl-’

  • stopping of the final sustainable consonant ‘-sh’, which has become ‘p’

Summary of phonological simplifying processes

As mentioned, there are many phonological simplifying processes. The most common are summarised in Table 1 below (the processes discussed in this article have been highlighted in red)



1 reduplication






consonant deletion


weak syllable deletion



cluster reduction











vowel harmony

consonant harmony

context-sensitive voicing

word final de-voicing


feature synthesis

Table 1. Phonological Simplifying Processes

Phonological disorders

Phonological disorders occur for two reasons:

  1. phonological processes persist beyond the age when most typically developing children have stopped using them
  2. the child’s particular processes deviate markedly from the expected pattern of phonological simplifications (in some cases, the child may be using an idiosyncratic rule system to govern how he or she uses phonemes in speech)

Remember that phonological disorders are phonemic in nature, whereas articulation disorders are phonetic, involving errors in pronouncing speech sounds. Children with phonological disorders may well be able to pronounce all speech sounds: their difficulty relates not to the physical articulation of speech sounds but the use of particular speech sounds in particular contexts within words.