In most languages, the consonant phonemes fall largerly into two basic classes: ‘obstruents’, including stops, affricates, and spirant, and ‘sonorants’, including nasals, liquids, and glide vocoids like English /w/ and /j/. [...]. Obstruents often constitute a neatly patterned system, involving contrasts of position and manner of articulation. Sonorants sometimes appear to be random left-over.
- Hockett (1958), a pag.97