Phonology refers to the rules we use to put sounds into words. We use these rules unconsciously, for example a typically developing child will quickly begin to know that e.g. sounds such as "h" or clusters such as "cl" only occur at the beginning of words or syllables (parts of words), whereas sounds like "ng" only occur at the ends of words or syllables.

Some children with language impairment or dyslexia may not be able to structure sound combinations to correctly make words. This can cause problems with spelling and reading words. This difficulty is a key feature of dyslexia and can often be found in children with language impairment.