Collins Cobuild English Grammar (183 page)

R7
      Some nouns that end with the sound
/θ/
, for example
mouth
, have their plural forms pronounced as ending in
/ð
Ζ
/
. With others, such as
bath
and
path
, the pronunciation can be either
/θs/
or
/ð
Ζ
/
. You may need to check the pronunciations of words like these in a Cobuild dictionary.

R8
      In most other cases the
s
is pronounced
/z/
.

bottle		bottles
degree		degrees
doctor		doctors
idea		ideas
leg		legs
system		systems
tab		tabs

R9
      With nouns that end in a consonant letter followed by
y
, you substitute
ies
for
y
to form the plural.

country		countries
lady		ladies
opportunity		opportunities

With nouns that end in a vowel letter followed by
y
, you just add
s
to form the plural.

boy		boys
day		days
valley		valleys