Glottalization is the production of sounds with completely closed glottis. This type of articulation is often found in English pronunciation. Voiceless consonants are articulated with open glottis in most cases and always in the case of fricatives where airflow is very important for successful production.
In glottalised pronunciation a glottal stop occurs just before p, t, k, or tʃ. It is only found in certain contexts and the rules are considered by the foreign learners of English too difficult to learn (at least from the practical point of view). However, I do not encourage any learner of English as a foreign language to spend too much time on this topic (unless the purpose of learning English is other than simple communication). Keeping to the more conservative pronunciation and not using glottalization is simpler.
Many learners, including some of my intermediate students have noticed the occurrence of this glottal stop sound and of course they wanted to know what is that they are hearing.
The glottal stop sound is represented by /ʔ/. It looks very similar with a question mark. The most widespread glottalization is that of /tʃ/ at the end of a stressed syllable.
|Word||With Glottalization||Without Glottalization|
|Catching||/ˈkæʔtʃ' ɪŋ/||/ˈkætʃ' ɪŋ/|
|Riches||/ˈrɪʔtʃ' ɪz/||/ˈrɪtʃ' ɪz/|
|Nature||/ˈneɪʔ' tʃər/||/ˈneɪ' tʃər/|
Similar glottalization can be found in the case of p, t, and k but this is not found so regularly. It normally happens when the plosive is followed by another consonant or a pause.
|Word||With glottalization||Without glottalization|
|Petrol||/ˈpɛʔ' trəl/||/ˈpɛ' trəl/|
Foreign learners do not usually learn this kind of pronunciation but many acquire it through speaking to English people. Knowing what is going on in the case of glottalized pronunciation is a good idea but again, without insisting too much on this matter.
Although I do not recommend teaching learners to produce glottalization of p, t, k, and tʃ, I have seen advance learners who were able to produce it and one of the reasons of the increase in naturalness in their accent seemed to be the effect of the usage of glottalization.