The spelling of /s/ is <s> initially or <c> in cymbal, and <s>, <ss> or <ce> medially or finally. The /Ɵ/ sound is spelled <th> throughout.
This contrast is between two voiceless fricatives. Among native speakers the replacement of /s/ with /Ɵ/ is known as a lisp (technically an interdental lisp) and is common among young children. The six-year-old Violet Elizabeth Bott in Richmal Crompton's Just William books is able to control William Brown with the threat "I'll thcream, then I'll thcream and I'll thcream and I'll thcream till I'm thick" (William in Trouble, 1927, p. 86). If it persists it is regarded as a speech defect and can be treated by speech therapists. It may be associated with effeminacy and was caricatured as aristocratic in eighteenth century comedy. Since rather few languages use /Ɵ/, the problem for EFL learners tends to be the reverse of the lisp, substituting /s/ for /Ɵ/.
Interesting pairs include:
Since /s/ is a common sound, the figure for the mean density is very low at 0.6%. The set makes 59 semantic contrasts, a loading of 61%. The relative scarcity of minimal pairs is slight evidence for the O'Connor hypothesis that language is self-repairing, since this is a troublesome distinction.
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John Higgins, Shaftesbury, August 2010.