 Sonority is a phonetic property that classifies speech sounds in terms of a hierarchy or scale. Articulatorily, speech sounds are defined as sonorant if the pressure of air behind the constriction is approximately equal to the ambient air pressure. This of course applies to vowels. Non-sonorant speech sounds are plosive and fricative consonants. Since here, the air pressure behind the constriction is much higher than the ambient air pressure. Acoustically, sonorant speech sounds are much louder. That is, they produce a higher amplitude than non-sonorant sounds. According to their amount of sonority, all speech sounds can be ranked where vowels involve a high degree of sonority, that is, the highest amplitude and equal air pressure, whereas plosives are lowest on the sonority scale. They involve the lowest amplitude and the biggest air pressure differences. In between, we have approximants, nasals, fricatives and affricates. Using distinctive features, we define vowels, approximants and nasals as plus sonorant and fricatives, affricates and plosives as minus sonorant. Furthermore, sonorant is a major class feature. The sonority scale is especially important in analyzing syllable structure and rules about what sound segments may appear in on-sets or codars.