The alveolar plosives /t/ and /d/ are the most unstable consonants in English. We’ve already seen that they are prime candidates for assimilation, and so are they for elision. As we said, elision means not to pronounce a phoneme, to drop it. It’s the easiest thing in the world, very convenient when that sound is difficult to produce because of the other sounds that surround it. The key question is, when are you allowed to drop the /t/ and the /d/?
There is a general rule that says that /t/ and /d/ are frequently dropped when they are found between consonants, unless the third consonant is a /h/.
Let’s see some examples:
As you can see, the /t/ and /d/ in left and cold are not pronounced.
But this doesn’t usually happen if the third consonant in the cluster is a /h/.
One crucial thing you have to keep in mind is that when we say /t/ and /d/ we are (as always) talking about phonemes, not letters. So the elision of these two sounds applies to -ed endings of pasts and participles as well. This might seem puzzling because then the inflectional mark of the past or participle is lost and those tenses sound exactly the same as the present. But this is the way it is and the possible ambiguity is normally resolved by the context. So, don’t hesitate to do the elision in -ed endings when the conditions are met.
Now let me illustrate the above with some examples. You’ll see how easily speakers do away with -ed pasts and participles without seemingly worrying about possible misunderstandings:
Hello, the Spanish Civil War was a defining war of the twentieth century. It was a brutal conflict that polarized Spain pitting the left against the right, the anti-clericals against the church, the unions against the landed classes and the republicans against the monarchists (Melvyn Bragg, BBC4).
And now one final comment to round things off. Elision is extremely common at word boundaries, that is, between different words, but it also works within individual words when there are three vowels in a row, as shown in the following examples: