The Approximants (Glides and Liquids)

• The glides (/j/ and /w/) and the liquids (/9r/ and /l/) in American English can be grouped together in a larger category called the approximants. This name comes from the fact that the articulators are brought into closer contact, or approximation, than in any of the vowels. However, the constriction is less than for the obstruents (fricatives and plosives).
• The glides /j/ and /w/ are similar to diphthongs in that they consist of vowel-like movements. They differ from diphthongs, which are moving vowels, in that:
  • Their energy is usually less than that that of a vowel.
  • Their formants do things which vowels never do.
    • In the case of /j/, F2 and F3 almost collide before going their separate ways. This near-miss leaves a characteristic X pattern which is the hallmark of the /j/. Think of /j/ as an exaggerated /i:/, where the tongue nearly touches the roof of the mouth. It may be divided into two phases: a period of maximal constriction followed by a rapid breakaway. Because the constriction for /j/ is so narrow, this phoneme is often marked by frication as well as voicing.
    • The phoneme /w/ usually starts as a single F1 at 200-400 Hz, with all significant energy below 800-900 Hz, and only gradually takes on very low F2 and F3 components as the following vowel unfolds. As soon as F3 is visible, however, it is above 2000 Hz, which helps distinguish /w/ from /9r/. Think of /w/ as a ``super" /u/, where the lips are nearly in the bilabial position, leaving only a small constriction from which something less than a vowel emerges. Lip rounding is an essential part of /w/, as with /u/. In addition, /w/ is also marked by a velar constriction.
    As usual with speech, these observations only represent the best-behaved examples of /j/ and /w/; we will see that there is a great deal of variation.
• We call these phonemes ``glides" because they glide into the syllable nucleus. They cannot form the nucleus of a syllable, and occur only in prevocalic position. When a glide follows a vowel within a syllable, the combination is considered a diphthong and not two separate phonemes.
• The liquids /9r/ and /l/ are among the most interesting of English phonemes. This is because of the position of the tongue which is in each case unique:
  •   In the case of /9r/, the retroflex liquid, the sides of the blade of the tongue are curled up to the alveolar ridge, and further back the tongue sides are brought into contact with the molars. These blockages force air to pass out through a narrow ellipse in the center of the mouth. The tip of the tongue may also be curled back; this is the original meaning of the word ``retroflexion", although different sorts of r-flavoring or rhotacization occur in the repertory of the world's languages: the uvular fricative in French ``rouge", a /d_(/-like flap in the Spanish ``pero", the trilled double r in the Spanish ``perro", and the real retroflexes in Hindi and other Indian languages.

    The main sign of the retroflex in spectrograms is that F3 comes very close to F2, in the extreme case being swallowed up into it, and in either case restricting all significant energy below 2000 Hz (higher in females and children). /9r/ is different from /3r/ in that in /9r/, the formants show a great deal of movement; in intervocalic position F3 will swing down below 2000 Hz and back above it. In /3r/, the formants seem to move instantly together and to stay there as long as the syllable persists.

  • The lateral liquid /l/ is in a sense the reverse of /9r/. In the lateral, it is the tip of the tongue which is placed on the alveolar ridge, while the sides of the tongue are left in their normal horizontal, open position. Air thus escapes from the two sides of the tongue out the mouth, but not from the center. The splitting and rejoining of the sound waves cause an antiresonance around 1500 Hz which is a good clue for /l/.

    The phoneme /l/ shows a lot of variety in the spectrogram. Before a vowel, F3 may descend or stay even, while F2 rises, giving the phoneme a forked appearance. This is particularly true for the syllable `ly' as in ``daily." In other cases, the formants F2 and F3 move directly into the next vowel without any marked frequency variations, but the /l/ shows less energy than the vowel. There is often a clear spectral discontinuity where the tongue touches the alveolar ridge, causing the antiresonance to form, and again when it is taken away. In postvocalic contexts, /l/ is signalled by the crushing down of F2 with F1 near or below 1000 Hz, with F3 simultaneously moving up toward 3000 Hz, again leaving the hole in the normal F2 range. The two cases may be combined in the case of intervocalic /l/, where an elliptical low-energy pattern may be detected. /l/ is easy to confuse with /oU/.

• One thing which /3r/ and /l/ have in common is that their duration can be as short or long as desired. The glides must move; we cannot pronounce a long /w/ or /j/; if we try to do so, they become /u/ or /i:/. But the liquids can be pronounced as long as we wish: try saying ``well" and draw out the /l/, or ``father" and draw out the /3r/. Both phonemes can become syllabic nuclei: for /l/ the symbol is /l_=/, while we have already seen the vowels /3r/ and /&r/.
• There are variants of the glides and liquids which occur in consonant clusters. Examples are the beginnings of the following words:
  • /s/ swipe, Sri, sly
  • /f/ few, foie gras, flood, from
  • /T/ thwart, thrice
  • /ph/ pew, poids, ply, pry
  • /th/ tune, twice, try
  • /kh/ cue, quiet, clay, cry
  • /b/ beautiful, bwana, blue, brute
  • /d/ dew, Dwight, dry
  • /g/ gewgaw, guava, glide, grind

  Notice that in English we do not like combinations such as /th l/ or /d l/, although these exist in other languages. The voiced /z/ and /v/ occur in very few such combinations; again, this is probably an English preference since there are words such as zouave and voir in French.

  In cases where the preceding consonant is voiceless, the glide or liquid may be partially or totally devoiced; in this case it is realized in aspiration bands rather than as voicing bands, and would be labelled phonetically as /j_0/, /w_0/, /9r_0/, or /l_0/. In all cases, the two phonemes interact and make recognition more difficult.

• Some phoneticians speak of the dark and light variants of /l/. What they call light /l/ might also be termed pre-vocalic /l/; while dark /l/ is post-vocalic. In cases of intervocalic /l/, the liquid will tend to group either with the preceding syllable, in which case it is dark, or with the following syllable, in which case it is light. But there are many cases where the distinction is not so clear, and we get elements of both, leading to the nice diamond or O shape between F2 and F3 which is an easy marker for /l/.

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