One blurry area is in segments variously called "semivowels", "semiconsonants", or "glides". On one side, there are vowel-like segments that are not in themselves syllabic, but form diphthongs as part of the syllable nucleus, as the "i" in English "boil" . On the other, there are approximants that behave like consonants in forming onsets, but are articulated very much like vowels, as the "y" in English "yes" . Some phonologists model these as both being the underlying vowel , so that the English word "bit" would phonemically be , "beet" would be , and "yield" would be phonemically . Likewise, "foot" would be , "food" would be , "wood" would be , and "wooed" would be . However, there is a (perhaps allophonic) difference in articulation between these segments, with the in "yes" and "yield" and the of "wooed" having more constriction and a more definite place of articulation than the in "boil" or "bit" or the of "foot".