Why are clusters such as /sk/ (as in sky), /st/ (stop), and /sp/ (spill) allowed as onsets in English? The sonority decreases in these clusters and does that not violate the phonotactic rules?

On a related note, it seems intervocalic clusters such as /ks/ are divided into two syllables instead of counted as the onset of the succeeding syllable: Anaximenes is usually syllabified as /ˌæ.nækˈsɪ.məˌniːz/ instead of /ˌæ.næˈksɪ.məˌniːz/, for example.

Perhaps the latter observation could be explained by rejecting the maximal onset principle, but when combined with the first observation, it seems to show that there is something special about /s/ (and perhaps sibilants in general) in English. I had trouble finding any explanation for this phenomenon, however.

Any insight is appreciated! Thanks for reading my question.

2 Answers 2


Syllables do not have to conform to the notion of "sonority sequencing", which is only a rough approximation of crosslinguistic syllable structure tendencies. It is generally recognized (following decades of argument by Ohala, also see Wright 1996) that abstract "sonority" is not particularly relevant in explaining segment sequence tendencies, and what matters is whether a sequence is easily parsed. The desirability of onset [tr] relative to [rt] or [tw, nw] relative to [wt, wn] can be explained by the fact that the former lead to acoustic landmarks which make it easy to identify the segments (in an onset), but the latter are not (for instance, [w] has very weak acoustic cues, no striking release, low amplitude, but a strong influence on vowel formants, so [w] "should" be next to a vowel). Sequences of the form [sC] where C is not a fricative are fairly easy to parse acoustically – though not trivial, so they might be allowed, or they might be disallowed. Sequences of the form [ʃC] would also be good, but having a constrast between [sC] and [ʃC] is not so good (because it is harder to distinguish the difference between [s] and [ʃ] before a consonant).

Since [ks] is not a possible onset in English, there is only one possible syllabification of /VksV/: [Vk.sV]. The maximum onset principle does some work for you, in explaining why /VstV/ syllabifies as [V.stV] in English, not [Vs.tV].

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    Does /VstV/ syllabify as [V.stV] in English? I think that would be controversial to the same extent that the syllabification of words like "city" is controversial. My impression was that the debate about syllabification of consonants after phonologically short/lax vowels (the ones that can't occur word-finally in a stressed syllable in a normal English word, like /ɪ/, /ɛ/, /æ/, /ʊ/, /ʌ/, and for British English speakers /ɒ/) is not entirely settled. Am I wrong? Aug 27, 2017 at 2:52
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    That is, is there actually now a consensus in favor of the syllabification of "city" as /sɪ.ti/ (and so on), and a rejection of the syllabification as /sɪt.i/ that was argued for by e.g. John Wells ("Syllabification and allophony", 1990)? I know that many of the phenomena Wells uses as evidence can also be accounted for by foot-based explanations, but I don't know if any knockdown arguments against the /sɪt.i/ type syllabifications have been discovered. Aug 27, 2017 at 2:56
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    Oops, to clarify my previous two comments–Wells does use V.stV division in words like "distort", where the second vowel is stressed, but I think he would use Vst.V division in words like "dusty", where the first vowel is stressed. (And Vs.tV division only in words like "distaste" where the [t] is aspirated). Also, I shouldn't have mentioned short/lax vowels in particular, because Wells argues for stress-based syllabification even in words with a "long" stressed vowel like "eating", so I assume he would also have Vst.V division in a word like "tasty". Aug 27, 2017 at 3:02
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    A basic problem with claims about syllabification is that there is no clear way to adjudicate questions of where to place the dot in XYZ (or even whether there is a dot). The concept of "consensus" as applied to syllabification studies has to be evaluated differently from questions about other well-understood and settled matters (nothing comes to mind at the moment). The OP assumes certain facts of syllabification, whereas I personally don't take the syllable itself for granted. So my answer is tuned to certain assumptions; but you're raising valid foundational questions
    – user6726
    Aug 27, 2017 at 4:21

The status of /s/ and sC clusters does indeed pose a problem for phonotactics. /sp, sk/ violate the sonority profile; /sl/ violates constraints against identical place of articulation (POA) in onset; /st/ violates both; and /sn/ violates three phonotactic constraints: sonority, POA, and sonority distance of onsets (other Cn onsets are not permitted in English). Furthermore, sC clusters permit different POAs in 2nd position e.g./sp, st, sk/; whereas POA is restricted in other onsets clusters, mostly coronal /r,l/ e.g. /pr,pl,tr,kr,kl/. In all these ways, /s/ behaves in a special way.

This has led some people to propose that /s/ is an appendix linked to a level higher than the syllable in prosodic structure (e.g. Goldsmith 1990). In the Government Phonology framework, /s/ in sC is considered to be a coda. This view is recently developed by Goad (2012) "sC Clusters are (almost always) coda-initial". Goad argues against the perceptually-based account by pointing out that cross-linguistically s+stop are the most common sC clusters. The perceptual cues to C in sC will be compromised by /s/; therefore, we would expect the most common sC to have a C with robust internal cues such as s+liquid.

Regarding /ks/: according to English phonotactics, this would be syllabified as /k.s/; otherwise, it would violate the sonority distance principle. In English, onset profiles cannot consist of stop+fricative or stop+nasal.

  • Why does /sn/ violate sonority? Isn't /n/ more sonorous than /s/, and more the more sonorous consonants would be expected to be closer to the nucleus?
    – b a
    Aug 8, 2018 at 22:35
  • Yes, you are correct. I was not clear in my answer. Here is the Sonority Hierarchy from least to most sonorous: Obstruants (stops, fricatives, affricates) < Nasals < Liquids < Glides < Vowels. Phonotactic restrictions in onset are seen as restrictions on "sonority distance". The distance between Obstr+Nas = 1, Obstr+Liquid = 2; Obstr+Glide = 3. English requires a minimal distance of 2, & thus doesn't permit Obstr+Nas onsets such as *pn,*gn. However, in English we do find /s/+nas clusters. So what I should have said is that /s/+nas clusters violate the Sonority Distance restrictions of English.
    – k8i
    Aug 10, 2018 at 15:22

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