Every word has a stressed syllable (sílaba tónica). For example, the word espa stresses the last syllable.
Word endings and written accents (tildes) provide a predictable guide to stress syllables in Spanish, allowing you to read any word correctly.
A. BASIC RULES FOR THE USAGE OF ACCENTS / REGLAS BÁSICAS DE ACENTUACIÓN
1. Words that end in a vowel, -n, or -s stress the next-to-last syllable: se, emen, sas.
2. Words that do not end in a vowel, -n, or -s, stress the last syllable: bon, pa, can.
Words that do not follow the above rules carry a written accent to show which syllable is stressed:
ca (does not follow rule 1: it ends in a vowel but stresses the last syllable)
emenes (neither the last nor the next-to-last syllable is stressed)
bol (does not follow rule 2: it does not end in a vowel, -n or -s, but still stresses the next-to-last syllable)
According to the basic rules, thus, you need two criteria to decide whether a word needs a tilde or not:a) its ending,b) which syllable is stressed.
The word región needs a tilde because
a) it ends with “n” but
b) the penultimate syllable is not stressed.
The word regiones does not need a tilde because
a) it ends with “s” and
b) the penultimate syllable is stressed.
B. OTHER USES OF THE WRITTEN ACCENT / OTROS USOS DE LA TILDE
3. The written accent also indicates stress on a weak vowel (i, u) that is followed or preceded by a strong vowel (a, e, o): dí·a, Ma·rí·a, Ra·úl, o·í·do, a·hí, ra·íz, mí·o, dú·o, ge·o·gra·fí·a
BUT: democia (the weak vowel “i” is not stressed, therefore rule 1 applies)
4. A written accent is not used for one-syllable words (fe, ti, tres, Dios), except to distinguish between certain words that are otherwise spelled identically, such as:
you (object pronoun)
Another common group of such pairs are words like que, which need a written accent when used as a part of a direct or indirect question:
|¿Qué dices? What …?
¿cómo llego? how …?
Sabe dónde estoy. He knows where I am.
|Digo qu hace calor I say …
cmo quieras as…
Estoy dnde te dije. I am where I told you.