# Y → e, o → u: sound-driven swaps

> id: grammar.conjunctions.y-e-o-u · category: grammar · depth: standard · levels: A1 · review: internally_reviewed

**Summary.** Y becomes e before the i sound (padre e hijo); o becomes u before the o sound (siete u ocho). Pure phonetics, automatic.

Two conjunctions change shape to avoid an awkward vowel clash. Y ('and') becomes e before a word beginning with the i sound (i- or hi-): español e inglés, padre e hijo, madre e hija. O ('or') becomes u before a word beginning with the o sound (o- or ho-): siete u ocho, uno u otro, ayer u hoy, mujeres u hombres.

The swap is automatic and phonetic — you're avoiding two identical vowel sounds in a row. It happens only directly before the relevant sound; elsewhere y and o are unchanged.

The crucial exception is sound, not spelling: before hie-/hia-, the h hides a diphthong (/je/), so the word doesn't actually start with the i vowel and y stays — agua y hielo, fibra y hierro, madera y hierro. Always test by ear.

## Examples
- Trabajo con padres e hijos. — I work with parents and children.
- ¿Serán seis u ocho personas? — Will it be six or eight people?
- Trabajo con padres e hijos, y atiendo de lunes a viernes. — I work with parents and children, and I'm open Monday to Friday.

Related: grammar.conjunctions.pero-sino

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