Phonological Development

Phonological Development refers to the way in which infants develop the ability to make sounds. You may have younger siblings or have  heard stories from your own childhood about mispronunciations of sounds and words as your are in the stages of learning to speak. ‘iter’ rather than ‘sister’ for instance.
Each language has a certain set of sounds that are used to make up its lexicon (word bank) known as phonemes. These phonemes are described as contrastive – that is they help differentiate between words. Bat, and sat differ in the phoneme sounds B and S.
When describing and analysing the sound systems linguists use the International Phonetic Alphabet. The reasons is that sometimes in the written form, letters are misleading about the sound they make. For instance the first phonemes in Cat and Kettle are identical but in letter form they differ. However in Roger and Dig the phoneme identified by the letter g makes a different sound. Think also of Y in silly and young.
The phonemes (or speech sounds) that we make are divided into two major types: Vowels and Consonants. In school we learn that the 5 vowels are A E I O U and that consonants are all the other letters. Linguistics however recognises that the difference lies specifically in the way the sounds are made.
Vowels are sounds with no obstruction to the airflow. The different vowels sounds are made by either coming from the front or back or the mouth (front and back vowels) as well as whether the jaw is open or closed (open and close vowels.) the vowel in cat for instance seems to come from the back of the mouth with an open jaw. In Kit however the vowel sound is made from further forward in the mouth with a jaw that is more closed.
Consonants are speech sounds that involve a momentary interruption or obstruction in the airlfow. These can be differentiated by there factors;

1. voice
2. place of articulation
3. manner of articulation