All languages follow a specific set of rules that determine how we sound when speaking. The study of these rules is called phonology.
One of the main focuses in phonology is contrast – which sounds can create a change in the meaning of a word? For example in English, the words ‘cap’ and ‘gap’ have different meanings, so the sounds [k] and [g] must be distinct phonemes. In many Aboriginal languages, there is no distinction between [k] and [g], they are the same phoneme (so are usually represented by a single letter, either ‘k’ or ‘g’).
The test for a phoneme in a language is to find two words which are identical in every respect except for one sound. The word will change in meaning depending on which of the two differing sounds is used.
Writing systems in Aboriginal languages (as in many other languages) are based on the phonological system of the language, with a separate symbol (or letter) for each sound (or phoneme). The English writing system is partly phonological, but has some symbols (such as ‘th’) that represent different sounds (think about the initial sounds in the words thin and then), and some sounds (such as [f]) which can be represented by different symbols (think about words like fun, laugh, phone, coffee).