A notoriously tough aspect for new cuers is assigning the correct handshape for /s/ and /z/. This decision occurs frequently in English because it affects plurals (e.g., cats, dogs, horses), posessives (e.g., Matt's, Pam's, and Rich's), as well as inflections for subject-verb agreement (hits, spills, washes). 

Rule

1) If the root word ends in a voiceless sound (e.g., rat), the -s ending is pronounced (cued) /s/. Exceptions to this will be noted below for voiceless sounds that need a vowel before adding the plural marker.

2) If the root word ends in a voiced sound (e.g., phone), the -s ending is pronounced (cued) /z/. This inclueds root words that end with vowels as all vowels are voiced. Exceptions to this will be noted below for voiced sounds that need a vowel before adding the plural marker.

3) Exceptions to the rules above are found in words that end in a type of sound called sibilants. It isn't necessary to know the term for these sounds, but it is worth knowing which phonemes are included: /ʃshshʃshshʃshsh/ (wish), /ʧchchʧchchʧchch/ (church), /sssssssss/ (bus), /zzzzzzzzz/ (buzz), /ʒzhzhʒzhzhʒzhzh/ (garage), and /ʤjjʤjjʤjj/ (judge). These words take a vowel, /ɪĭiɪĭiɪĭi/ or /əəəəəəəəə/, before /zzzzzzzzz/**. Selection of /ɪĭiɪĭiɪĭi/ or /əəəəəəəəə/ in the examples below is not meant to suggest a preference for either vowel for that particular word. Note that, inspite of spelling, these final syllables do not take the vowel /ɛěehɛěehɛěeh/. 

** You do not need to commit to either /ɪĭiɪĭiɪĭi/ or /əəəəəəəəə/ for these plural endings. In reality, you are likely to alternate between the vowels depending on whether the word is cued alone or in a sentence and whether the word is stressed or not. For example, one may say the single word bushes as /bbbbbbbbbʊo͝oooʊo͝oooʊo͝oooʃshshʃshshʃshshɪĭiɪĭiɪĭizzzzzzzzz/, but they same cuer may pronounce the word with a schwa when it occurs in a sentence, The bushes need a good watering.

Instruction

When learning to discriminate between two building blocks, it can be useful for instructors to choose words that differ only in that one way. So when teaching students to discriminate /s/ and /z/, examples like rice and rise may be more effective than cats and dogs. In this way, students can overcome interference from spelling (i.e., recognize that the letter "s" is not always cued as /s/) if switching a /z/ to an /s/ makes a new word. So when students consider how to cue eyes, they may realize that cueing the word with a final /s/ actually makes the word ice.

fleece	fleas
lice	lies
gross	grows
race	rays
dice	dies
muscle	muzzle
pace	pays
source	sores
face	phase
loose	lose
noose	news
sauce	saws
juice	Jews

New cuers who use speech to figure out how to cue must be reminded not to whisper when trying to identify /s/ and /z/. Whispering is the turning off of the vocal fold vibration. By whispering, one changes instances of /z/ to /s/!

Teaching Deaf and Foreign Speakers

Teaching people to discriminate /s/ and /z/ presumes that they already have the building blocks of the English language in their minds. For those students, they must learn to re-examine what they take for granted. Some students, including some deaf students and English Language Learners, may not already have these building blocks established in their minds. For them, they will be learning the cues and the patterns of English at the same time. This process more resembles learning English as a foreign language than traditional CS classes taught to hearing English speakers.

Acquiring English Morphology

For deaf children who acquire English through cueing, this rules is obviously not taught. rather, the rules of English morphology (along with its variations) are acquired passively. 

Links

• /s/ vs. /z/ Quiz The Quizzes and Games section of DailyCues.com has an interactive quiz. Ten words are randomly chosen from a bank of words. You must decide which handshape would be used for the phoneme represented by the letter "s" (e.g., music). 
• On Being: Take the "Wug" Test Linguist Jean Berko Gleason famously uncovered how people generalize endings in her "wug" test. This blog entry with reflections from readers sheds light on this phenomenon that cuers share in.