Elision is when under certain circumstances sounds disappear. In more technical language, specialists will say that in certain circumstances a phoneme may be realized as zero, have zero realization, or be deleted.
As in the case of assimilation, elision appears in casual, rapid speech which leads to change in phoneme realization. Foreign learners of English don’t usually learn elision (it is considered unnecessary) but in my opinion it is very important for foreign learners of English to be aware of elision and of how native speakers of English talk to each other. This is because a foreign learner of English might expect to hear certain sounds but he doesn’t, which leads to confusion. Many learners think that their teacher taught them wrong pronunciation because what he knows is not what he hears, in movies for example.
We will look at some examples now but bear in mind that there are many possibilities and just a small number of examples can be given here.
In words like "today" and "perhaps" the vowel in the first syllable may disappear because of the aspiration of the initial plosive which can take up the whole of the middle of the first syllable.
Today – /təˈdeɪ/ becomes /tˈdeɪ/
Perhaps – /pərˈhæps/ becomes /pˈhæps/
Basically, the vowel in front of "n", "l", or "r" is not pronounced, so the word begins with two consonants. This creates a great confusion among Vietnamese learners.
Police – /pəˈlis/ becomes /pˈlis/
Tonight – /təˈnaɪt/ becomes /tˈnaɪt/
In clusters of three plosives or two plosives and a fricative, the middle plosive sound might disappear as is shown in the examples below.
Looked back – /lʊkt bæk/ becomes /lʊk bæk/
Scripts – /skrɪpts/ becomes /skrɪps/
It is known that the word "of" is pronounced /ʌv, ɒv; unstressed əv/. Well, the /v/ sound disappears if the word "of" is followed by a word that starts with a consonant.
Lots of cars – /lɒts ʌv kɑrs/ becomes /lɒts ə kɑrs/
Waste of money – /weɪst ʌv ˈmʌni/ becomes /weɪst ə ˈmʌni/
Some authors consider contractions as examples of elision but I will set them apart since they are very common in speech and writing, and they are represented with special spelling forms.