From the archives...
The following question was originally posted on the (now discontinued) LOE Forum.
Why does s sound like it is saying "sh" in sure? Are there any other words where s says "sh"?
It is called assimilation, and it's actually somewhat common with certain sounds, though it only rarely happens at the beginning of a word like this.
In "sure," the /s/ sound "assimilates" to the following U sound, taking a shape closer to that sound and pronounced in the same area of the mouth so that it is easier to say. Other sounds, such as /t/, /d/, and /z/, also assimilate before a U in some words.
Here are some examples:
/t/ to /ch/ - picture, architecture
/d/ to /j/ - education, arduous
/z/ to /ZH/ - azure, usual, measure
In LOE curriculum, the concept of assimilation is introduced in Foundations D lesson 150 and in Essentials lessons 28 and 29.