Variable and invariable words r Variable words have inflective endings,i.e.part of the word remains constant while the other part changes regularly to fulfill different grammatical functions. happy---happier---happiest interest---interesting---interested Invariable words,such as since, when,hello,do not have inflective endings.Variable and invariable words Variable words have inflective endings, i.e. part of the word remains constant while the other part changes regularly to fulfill different grammatical functions. happy---happier---happiest interest---interesting---interested Invariable words, such as since, when, hello, do not have inflective endings