Main spellings (~95%)
⟨s⟩ ~55%
The most common spelling — works almost anywhere.
⟨ss⟩ ~10%
Doubled after short vowels.
⟨c⟩ ~25%
Before ⟨e⟩, ⟨i⟩, or ⟨y⟩, the letter ⟨c⟩ makes the /s/ sound (not /k/).
The soft C rule: ⟨c⟩ makes /s/ before ⟨e⟩, ⟨i⟩, or ⟨y⟩ (cell, city, cycle). Before ⟨a⟩, ⟨o⟩, ⟨u⟩, or consonants, it makes /k/ (cat, come, cup, class). This rule is very reliable!
⟨ce⟩ ~5%
Word-finally, ⟨ce⟩ spells /s/ with a silent ⟨e⟩.
Unusual spellings (~5%)
⟨sc⟩
In a few words, ⟨sc⟩ before ⟨e⟩ or ⟨i⟩ makes /s/ (the ⟨c⟩ is silent).
Two ways to see this: You can think of ⟨sc⟩ as an unusual spelling of /s/, or as a silent ⟨c⟩ after ⟨s⟩. Both are valid. See the full list on the
silent C page.
⟨ps⟩
At the start of words from Greek, the ⟨p⟩ is silent.
Two ways to see this: You can think of ⟨ps⟩ as an unusual spelling of /s/, or as a silent ⟨p⟩ before ⟨s⟩ — see the
silent P page for the full list. Both are valid.
/s/ vs /z/
Don't confuse /s/ with /z/! The letter ⟨s⟩ can make either sound. Word-initially, it's usually /s/ (see, some). Between vowels or word-finally after voiced sounds, it's often /z/ (is, his, these). Compare: seal vs zeal, price vs prize.