vowel or a syllabic consonant . The American linguist Kenneth Pike (1943) suggested the terms "vocoid" for a phonetic vowel and "vowel" for a phonological vowel, so using this terminology, and are classified as vocoids but not vowels. However, Maddieson and Emmory (1985) demonstrated from a range of languages that semivowels are produced with a narrower constriction of the vocal tract than vowels, and so may be considered consonants on that basis. Nonetheless, the phonetic and phonemic definitions would still conflict for the syllabic /l/ in table or the syllabic nasals in button and rhythm. Articulation The traditional view of vowel production, reflected for example in the terminology and presentation of the International Phonetic Alphabet, is one of articulatory features that determine a vowel's quality as distinguishing it from other vowels. Daniel Jones developed the cardinal vowel system to describe vowels in terms of the features of tongue height (vertical dimension), tongue backness (horizontal dimension) and roundedness (lip articulation). These three parameters are indicated in the schematic quadrilateral IPA vowel diagram on the right. There are additional features of vowel quality, such as the velum position (nasality), type of vocal fold vibration (phonation), and tongue root position. This conception of vowel articulation has been known to be inaccurate since 1928. Peter Ladefoged has said that "early phoneticians... thought they were describing the highest point of the tongue, but they were not. They were actually describing formant frequencies." (See below.) The IPA Handbook concedes that "the vowel quadrilateral must be regarded as an abstraction and not a direct mapping of tongue position." Nonetheless, the concept that vowel qualities are determined primarily by tongue position and lip rounding continues to be used in pedagogy, as it provides an intuitive explanation of how vowels are distinguished. Height Theoretically, vowel height refers to the vertical position of either the tongue or the jaw (depending on the model) relative to either the roof of the mouth or the aperture of the jaw. In practice, however, it refers to the first formant (lowest resonance of the voice), abbreviated F1, which is associated with the height of the tongue. In close vowels, also known as high vowels, such as and , the first formant is consistent with the tongue being positioned close to the palate, high in the mouth, whereas in open vowels, also known as low vowels, such as , F1 is consistent with the jaw