the scale, open vowels, has the most air used for vibrations, and the bottom of the scale has the least air being used for vibrations. That can be demonstrated by putting a few fingers on one's throat and pronouncing an open vowel such as the vowel [a], and then pronouncing one of the plosives (also known as stop consonants) of the [p t k] class. For vowels, there is a consistent level pressure generated from the lungs and diaphragm, and the difference in pressure in one's body and outside the mouth is minimal. For plosive, the pressure generated from the lungs and diaphragm changes significantly, and the difference in pressure in one's body and outside the mouth is maximal before release (no air is flowing, and the vocal folds are not resisting the air flow). More finely-nuanced hierarchies often exist within classes whose members cannot be said to be distinguished by relative sonority. In North American English, for example, the set /p t k/ has /t/ being by far the most subject to weakening when before an unstressed vowel (the usual American pronunciation has /t/ as a flap in later but normally no weakening of /p/ in caper or of /k/ in faker). In Portuguese, intervocalic /n/ and /l/ are typically lost historically (e.g. Lat. LUNA > /lua/ 'moon', DONARE > /doar/ 'donate', COLORE > /kor/ 'color'), but /r/ remains (CERA > /sera/ 'wax'), but Romanian has transformed the intervocalic non-geminate /l/ into /r/ (SOLEM > /so̯are/ 'sun') and reduced the geminate /ll/ to /l/ (OLLA > /o̯alə/ 'pot'). It has, however, left /n/ (LUNA > /lunə/ 'moon') and /r/ (PIRA > /parə/ 'pear') unchanged. Similarly, Romance languages often have geminate /mm/ weaker than /nn/, and geminate /rr/ is often stronger than other geminates, including /pp tt kk/. In such cases, many phonologists refer not to sonority but to a more abstract notion of relative strength. The latter was once posited as universal in its arrangement, but it is now known to be language-specific. Sonority in phonotactics Syllable structure tends to be highly influenced and motivated by the sonority scale, with the general rule that more sonorous elements are internal (i.e., close to the syllable nucleus) and less sonorant elements are external. For instance, the sequence /plant/ is permissible in many languages, while /lpatn/ is much less likely. (This is the sonority sequencing principle). This rule is applied with varying