I am confused about this question for long time but no internet resource explains about this.

Ok, when we have a consonant followed by an vowel in a pronunciation then for sure we have to fully aspirate the sound of that consonant. For example, in has /hæz/, we will fully aspirate /z/. That is meaningful. No problem right.

Now, when we have 2 consonants standing next to each other and at the end of a pronunciation, then my question is:

Should we fully aspirate both of these 2 consonants?

For example, in books /bʊks/, should we fully aspirate /k/ and then fully aspirate /s/. So, to pronounce /bʊks/, we will make 3 sounds:

-fully aspirate /bʊ/

-fully aspirate /k/

-fully aspirate /s/

Note: fully aspirate means fully pronounce (a sound) with an exhalation of breath. For example, when you fully aspirate /k/ (see video here https://www.youtube.com/watch?v=RhS65K59ogA, the lady made the /k/ sound in the time of 0:24)


Should we fully aspirate the last consonant only and the before consonant should be in the starting position and your tongue will make the sound of the last consonant from that starting position?

For example, in books /bʊks/, when we finish the sound /bʊk/ the back of the tongue will touch the soft palate and at that point of time we won't release the tongue to make the sound /k/ but release the tongue to the /s/ position to make the /s/ sound.

I believe that if we make the sound like that then it will be different from when people won't put their tongue at the /k/ position but after /bʊ/ they will make /s/ immediately and it will sound like /bʊs/

Ok, to make my question clearer, I recorded my voice so that you can imagine what I am asking about:

This voice shows the /bʊks/ with aspirate of both /k/ and /s/. See https://drive.google.com/file/d/0B9o9iLQ2SktLUHpmcnF2TFRCRTg/view?usp=sharing

This voice shows the /bʊks/ with aspirate of /s/ only. See https://drive.google.com/file/d/0B9o9iLQ2SktLQVNMc0ZZSUhVaXM/view?usp=sharing

I think this is a very interesting question!

  • 1
    I’m not quite sure what you’re really asking here; your last two paragraphs are very difficult to understand clearly. Yes, you should pronounce both the /k/ and the /s/ in books; but the release of the /k/ is usually done with the tongue already in position for the /s/, so there is little audible release. I don’t understand what you mean by “fully pronounce /k/ which sounds like /kə/”, though: /k/ and /kə/ sound different in English (/s/ and /si/ even more so). You cannot just add a vowel at the end—that changes what the word is; e.g., [pʰaɪk] is pike, but [ˈpʰaɪkə] is pica. Jul 2, 2015 at 9:39
  • No, we don't pronounce the penultimate consonent 'fully', if that's what you're asking. Bones isn't pronunced the same as bonus.
    – Tushar Raj
    Jul 2, 2015 at 9:46
  • 1
    You really need to hear these words pronounced, say by BBC newsreaders. Jul 2, 2015 at 9:46
  • @ Janus, I edited my question. I mean: fully pronounce means you can hear the sound. For example, when you fully pronounce /k/ it will sound like like /kə/ (see video here youtube.com/watch?v=RhS65K59ogA, , the lady made the /k/ sound in the time of 0:24)
    – Tom
    Jul 2, 2015 at 10:30
  • 3
    /k/ is aspirated at the beginning of words (like king), but it's not aspirated in books or skin. So it's not pronounced the same as at the beginning of the word. But it's still pronounced in that you can hear it. Jul 2, 2015 at 11:21

3 Answers 3


After your edit and the clarification the comments to the question have brought about, it is now much clearer what it is you’re asking here.

The simple answer is no.

Generally speaking, plosives in English are mandatorily aspirated [pʰ tʰ kʰ] when they come at the start of a stressed syllable, or (usually) word-initially. In all other cases, they are usually non-aspirated [p t k], though they may sometimes optionally be aspirated for effect.

Aspiration here refers to a short period of time after the closure in the oral cavity that blocks the airflow is released, but before your vocal cords start vibrating to produce a voiced sound. During the aspiration phase, also known as the voice-onset time, there is airflow, but no voice; you’re essentially pronouncing a [h]. When a /k/ comes at the start of a stressed syllable, the voice-onset time in English tends to be somewhere around 80 ms. Even in unaspirated plosives, your vocal cords don’t start vibrating immediately: unaspirated /k/ normally has a voice-onset time of about 15–20 ms in English.

In the example you give, books, the /k/ comes in the syllable coda, and as such is not normally aspirated. If you really want to emphasise that you’re saying books and not boogs, then you can aspirate the /k/ and say [bʊkʰs], but that is not very common, so use it sparingly.

However, the sound that follows /k/ here is a voiceless fricative and therefore by definition entails a continuous unvoiced airflow, just like regular aspiration does. The only difference is that in /s/, the unvoiced airflow is restricted by the position of the tongue against the roof of the mouth, with only a narrow hole the air can pass through.

When your tongue transitions from [k] to [s], the back of the tongue has to ‘let go’ of the soft palate, while the blade of the tongue in front has to ‘catch’ the alveolar ridge. These two movements are naturally difficult to time exactly, and it is very common that the first takes place perhaps 40–50 ms before the second. During that period, you do likely have some aspiration of the /k/; but it is not really noticeable, because it is shorter than the ‘full’ aspiration we find in can [kʰan] (perhaps half as long), and it tends to blend in with the sibilant airflow of the following /s/.

  • interesting answer. About your last paragraph, what if we don't aspirate the /k/ whatsoever (ie, we don't put the back of the tongue at the soft palate after /u/ in /bu/) and make the tongue immediately jump to /s/ position (ie, the front of the tongue catch the alveolar ridge to make the /s/ sound)? If that is the case, then it will sound like /bu s/. So then what is the difference between "/bu s/" & "/buks/ with /k/ not be fully aspirated"? very interesting question right?
    – Tom
    Jul 2, 2015 at 13:26
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    That wouldn’t be not aspirating the /k/—that would just be leaving it out altogether, which would give an entirely different word. Actually, since [bʊs] isn’t a word (except in certain northern English dialects), it would in general give something that’s not a word at all. But if we take bucks as an example instead and don’t put our tongue against the soft palate at all when pronouncing that, we would not be saying bucks but simply bus. Some consonant clusters are frequently simplified, but final /Vks/ (V = any vowel) is not one of them; the /k/ must be pronounced. Jul 2, 2015 at 13:33
  • This should probably go on the other posting, but it also seems relevant here: the aspiration becomes more obvious when one considers homophone(?) pairs like face topping and faced hopping, but probably not face stopping which should lack it. You can also play games with devoicing assimilation in related cases
    – tchrist
    Jul 3, 2015 at 3:17
  • I think there is a rule "if a stop followed by a consonant don't release the stop, but hold it", see my answer and give comment if you want to
    – Tom
    Jul 3, 2015 at 15:47
  • This is really really interesting! Do you know of good book/article references or youtube videos that go into these details about how vowels and consonants are produced, how and in duration aspiration happens, etc. for someone new to this? Feb 17, 2020 at 17:47

First, leading consonants are not always sounded. Almost, but not always. For instance, the "h" in honor and honest is, except in Cockney, completely silent.

Second, there are several consonant combinations which are used to express sounds which are only faintly related to the components. "ng" is prounounced entirely at the back of the mouth, with none of the pressure at the tip of the tongue which is used in pronouncing a separate "n". "Pt", as in "apt" is pronounced as a single plosive, with no aspiration at all. Consider the difference between "apt" and "appetite". "Th" as in "breath" is also pronounced as a single sound, rather than anything like a sequence of different phonemes. Likewise with "nk" as in hunk. There are various others, as well.

If you are referring to trailing consonants which are added to existing words, particularly "s" and the d in "ed", the degree of unvoiced exhalation separating the two depends entirely on the mechanics of the sounds involved. In the case of books, for instance, the glottal stop which characterizes "k" makes it difficult to transition to "s" without a bridging exhalation. For "ts", on the other hand, as in "bets", all that is required to produces the "s" is to release pressure on the tip of the tongue. Since the tongue pressure blocked all exhalation, there is no unvoiced exhalation preceding the sibilant - any exhalation at all produces the "s".

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    I think that the Original Poster is using the terms vowel and consonant with their phonetic and phonemic sense, not the orthographic one. In that system there is no consonant at the beginning of the word hour. Jul 2, 2015 at 13:50

I think I found the answer. So simple, that is the rule of stop consonant.

if a stop followed by a consonant don't release the stop, but hold it

See this video at time of 19:53 https://www.youtube.com/watch?v=cPvmjom0hwY&index=3&list=PLTx3GskMNoe-RRIzJpBKscBJEZk8E9zzZ

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    That woman doesn't know what she's talking about—or she's oversimplifying. She's conflating release and aspiration of plosives, at any rate. The rule she gives here is true of homorganic consonants, but not heterorganic ones. In pop music, the p is not released, but in_pop song_ or pop list it is. It is not aspirated, but it is released. Also note that she aspirates the final p in pop when she says it in isolation, which is misleading: that is only done when you wish to emphasise the sound, not in normal speech. Jul 3, 2015 at 15:54
  • she is very famous, she got 20 years of teaching pronunciation
    – Tom
    Jul 3, 2015 at 16:45
  • I believe she is right cos her theory is simpler but no other source from internet discuss about this
    – Tom
    Jul 3, 2015 at 16:45
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    In that case, she’s presumably simplifying things for her students. Or alternatively, just because she teaches pronunciation doesn’t mean she’s a phonetician. The rule as she gives it here is not correct. Stop are not automatically unreleased before any other consonant. Also whether a theory is simple or not is not relevant to whether it’s correct or not. Jul 3, 2015 at 16:51
  • but i feel it is much easier for me to speak a word, for example, "books" by holding the /k/ and release the /s/. Applying that rules for "pop music" , "job market", "had this",... I feel it very natural. If i have to fully release all these stop consonants (the ones before other consonant) then my speaking is a bit of clumsy and hard and somewhat unnatural
    – Tom
    Jul 3, 2015 at 16:58

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