1. What is phonetics? The (scientific?) study of speech. But why do we want to study speech?
2. The Primacy of Speech: speech is the primary way in which linguistic information is communicated between people. There are only two ways of linguistic communication that are natural (biological, independent of culture?): speech and sign (among the congenitally deaf and in some hunter-gatherer societies). Of these, speech is more widespread.
3. Naturalness of speech
2 In world society: languages with established writing systems are numerically a small minority. Most languages are unwritten (or were until this century).
3 In human development: children without disabilities acquire speech as a natural human function, e.g. like walking or eating. It does not require explicit instruction, is biologically pre-programmed, and is achieved to an equal degree of mastery by everyone (though some become more eloquent in what they have to say than others!)
4 In the development of literary languages: a literary language is a socially established forms of what was, at an earlier stage, merely one spoken dialect among many.
5 In quantity of activity: most linguistic activity is in the spoken medium. Indeed, even among literate people, writing is a relatively rare activity.
2 Articulatory phonetics: the organs of speech, the ways in which they may move and be coordinated with each other, and the possibilities for speech that this permits. These aspects can be observed to a certain extent by proprioception, assisted by training, as well as physiological and experimental studies.
3 Acoustic phonetics: how air is set in motion, made to vibrate and how speech waves are transmitted between speakers. In transmission, speech acoustics may be studied in incredible detail just by careful listening, or with instruments, such as the microphone, and a small computer.
4 Auditory phonetics and speech perception. Primarily based on psychological experiments and some physiological studies.