• By adding –s if there is a vowel before the -y
• By changing –y into –ies if a noun ends in a consonant before the -y.

Singular	Plural
analysis	analyses
axis	axes
basis	bases
crisis	crises
diagnosis	diagnoses
ellipsis	ellipses
hypothesis	hypotheses
oasis	oases
parenthesis	parentheses
thesis	theses

• By adding –s if there is a vowel before the -y
• By changing –y into –ies if a noun ends in a consonant before the -y.