Usually after “short” vowels.
VC and CVC | CCVC | With consonant digraphs | After vowel sound /ar/ spelt a (in Aust and southern UK accent) | Polysyllabic words |
ass (donkey) bass (fish) Bess boss Cass cuss doss fuss goss Hass (avocado) hiss Jess joss kiss lass less loss mass mess miss moss muss Ness piss poss sass suss Tess toss Yass  But s as in bus (last column) | bless bliss crass cress cross dress dross floss gloss press stress | chess | brass bypass class glass grass pass surpass | abbess access across actress address amass amiss assent assert assess asset assist assort assume basset blossom bossy carcass (US) caress cissy confess cosset darkness dressy duress egress emboss endless essay excess express fitness fortress fossil fussy glossy goodness gossip harass harness illness impress jackass madness mattress morass possess possum princess process profess progress recess regress repress ruthless sadness sickness success suppress unless weakness wireless witness |