Vowel Alternations: Define and Definition

Recognize how a long vowel in a base word becomes short in a related longer word.

Many English word pairs show a vowel alternation: the base word has a long vowel, and the related longer word has a short vowel, even though the spelling barely changes. Define has a long i (dih-FINE); definition has a short i (def-ih-NISH-un). Nation has a long a; national has a short a. Sane becomes sanity, crime becomes criminal, serene becomes serenity, please becomes pleasant. These shifts happened centuries ago and English spelling kept the old forms, so the vowel letter stays the same even as the sound changes.

Worked example: you hear 'divinity' in a lecture and are unsure how to spell the second vowel. Think of the base word, divine, with its clear long i. The spelling is i, so you write divinity. The alternation also works in reverse for decoding: if you see 'serenity' and recognize 'serene' inside it, you know its meaning even though it sounds different.

• 1Long vowels in base words often become short in longer forms.
• 2The spelling stays the same despite the sound change.
• 3Use the base word to spell and decode the longer form.