When to Change 'Y' to 'E' and 'O' to 'U' in Spanish

Changes keep conjunctions from blending with the word that follows

Two young children inside an igloo that they have built in their garden. The Igloo is lit from within.
Está enteramente construido de nieve y hielo. (It is built completely of snow and ice.). Paul McGee/Getty Images

Two of the most common conjunctions in Spanish — y (meaning "and") and (meaning "or") — can change spelling and pronunciation based on the word that follows. In that way, they are much like the "a" of English changing to "an" before a vowel sound.

Why Change Vowels?

Both changes help keep the conjunction from blending into the following word. Y becomes e when it precedes a word that begins with the i sound, while o becomes u when it precedes a word that begins with the o sound.

Typically, then, the y becomes e when it precedes most words that begin with i- or hi-, and o becomes u preceding words starting with o- or ho-.

When Not to Change Vowels

Y does not change before words, such as hierba, that begin with the ia, ie, io or iu sound, regardless of spelling.

Examples of Different Spanish Conjunction Forms

Here are a few examples of how to use what we've just learned:

  • Reciben tratamiento cruel e inhumano. (They are receiving cruel and inhumane treatment.)
  • Vendemos productos de limpieza e higiene. (We sell cleaning and hygiene products.)
  • Está enteramente construido de nieve y hielo. (It is built completely of snow and ice.)
  • Usamos punto y coma para separar las frases u oraciones que constituyen una enumeración. (We use a semicolon to separate phrases or sentences that make up a list.)
  • No recuerdo si fue ayer u hoy. (I don't remember if it was yesterday or today.)