I noticed this in many words e.g. puLP, the cluster /lp/ can take place in final position but not front.

e.g. 2. paRT but /rt/ can't take first place why?

  • 1
    I guess it gave us some evolutionary advantage over people whose words started LP... and RT...! Commented Dec 13, 2020 at 8:22
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    @OldBrixtonian you may be an adaptationist goat
    – James K
    Commented Dec 13, 2020 at 10:48
  • @James K <g> I like the cartoon but I'd never understand that adaptationist stuff. Lpointless rtrying. Commented Dec 13, 2020 at 14:45
  • (in case its not obvious, it is Darwinist cartoon that parodies the point of view that "every behaviour has a reason based on evolution, that all behaviour is "adaptive"... The goat would claim that we must have evolved to put "lp" at the end of words not the start, probably because it somehow helped us to attract a mate... which is obviously wrong)
    – James K
    Commented Dec 13, 2020 at 16:17

1 Answer 1


I won't go into details, but here's a brief account of how consonants are arranged in consonant clusters:


Every language has a unique set of rules called Phonotactic rules (or Phonotactic constraints) that govern the possible sequences of sounds in a particular language—that is, licit and illicit sequences of sounds. In other words, what sounds go together and where can they be found.

A sequence that is allowed in one language may be disfavoured in another language for instance, the cluster /pn/ is phonotactically well-formed in Greek, but ill-formed in English, that's why the /p/ in pneumonia is silent in English.

Over time, a language may undergo phonotactic change, for example, the /k/ in the word knight wasn't always silent as it is in Modern English, it was pronounced until Modern English.

Some of the constraints on syllable structure in ModEn are:

  • No PLOSIVE + NASAL sequence in a single syllable
  • No [ŋ] in the onset
  • No PLOSIVE + FRICATIVE in onsets
  • Obstruents in the coda must agree in voicing
  • No geminate in a single syllable

and many others....


There's a concept of Sonority, which is a relationship between sounds and how they are arranged within syllables.

Sonority Hierarchy

A sonority hierarchy is a hierarchical ranking of speech sounds. A typical order of Sonority values is:

Vowels > Glides > Liquids > Nasals > Fricatives > Affricates > Plosives

It means that vowels are the most sonorous and plosives are the least sonorous sounds. Vowels ([ɑ æ i ɪ ɔ u] etc), glides ([j w]), liquids ([l ɹ]) and nasals ([m n ŋ]) are called sonorants, while the rest are called obstruents.

Sonority Sequencing Principle

In phonology, we have a rule called Sonority Sequencing Principle which states that sounds rise in sonority from the onset (beginning of a syllable) to the nucleus and fall from the nuleus to the coda (end) of a syllable.

Here's a Sonority graph that illustrates how SSP works:

Sonority graph
From Wattpad

It's a sonority graph for 'trust' [tɹʌst]. Sonority should rise from the onset to the nucleus (usually a vowel) and then fall from the nucleus to the coda, which is indeed the case in [tɹʌst]:

  • [tɹ] → onset, Sonority rises from [t] to [ɹ]
  • [ʌ] → nucleus, Sonority rises from [ɹ] to [ʌ]
  • [st] → coda, Sonority falls from [s] to [t]

The reason why certain clusters don't occur at the beginning of a syllable is because they violate the Phonotactics of English (Sonority Sequencing Principle).

The cluster /lp/ can occur at the end (coda) because it's concordant with the SSP; the Sonority falls from /l/ to /p/ (Sonority should fall in the coda).

However, it does not occur in the onset because the sonoriy falls from /l/ to /p/ rather than rising (Sonority should rise in the onset).

The cluster /pl/ occurs in the onset because the sonority rises now, but it doesn't occur in the coda because the Sonority rises and in the coda position, the Sonority should fall.

There are lots of other restrictions and exceptions like clusters with /s/, but I'm not going to discuss it further.

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