Background

Most often, the /s/ sound in the initial, final, and medial positions is made by the consonant s as in set, sap, sand, bus, and beside. The use of the consonant s is very consistent for the /s/ sound, although there are other letters and combinations of letters that also make the /s/ sound. These include c in the words circus and circle, and the ps combination as in psychology. Sometimes the consonant s is silent, for example, when it is doubled in words like mess and dress.  

The consonant s can make other sounds, such as the /sh/ sound in sugar, or the /z/ sound in easy, rose, dogs, and is. When followed by c, the sc combination can make the /sk/ sound as in scare, or the c can be silent as in scent.