Irregular –sis / -ses Nouns
As you know, for most English nouns, making them plural is as simple as adding -s or -es to them. However, there are nouns in English whose singular form ends in –sis, and the rule of adding -s / -es does not apply. These words come from Greek or Latin, and they are what we call irregular nouns. To make them plural, change -sis to -ses. Take a look at the examples below:
analysis – analyses
axis – axes
basis – bases
crisis – crises
diagnosis – diagnoses
ellipsis – ellipses
parenthesis – parentheses
prognosis – prognoses
synopsis – synopses
thesis – theses
Note that we pronounce the singular ending –sis as /sɪs/, and the plural ending –ses as /siz/.
Joanna Rodzen-Hickey has been an ESL teacher and consultant for nearly 20 years. She has taught English at numerous universities and community colleges in New Jersey and currently teaches at the Hackettstown High School in Hackettstown, NJ.