Phonetic theory regards the nature of sounds in speech (called phones) and how they are made, heard and thought of. Phonology, which came from it, studies sound systems and sound units (such as phonemes and distinctive features). Phonetics is one of the two parts of orthographical linguistics, the other part being spelling, differing from grammar and lexis.
Phonetics has three main branches:
- articulatory phonetics, regarding the place of articulation and the movement of the lips, tongue, vocal tract, and vocal folds,
- acoustic phonetics, concerned with the traits of the sound waves and how the inner ear hears them, and
- auditory phonetics, concerned with speech perception (mostly how the brain thinks of what the ears hear)
The first time phonetics was studied was 2,500 years ago in what is now India, with Pāṇini, when he wrote about the place and manner of articulation of consonants in Sanskrit in his 5th century BC essay on Sanskrit linguistics. The major Indic scripts today order their consonants the way Pāṇini did.