Default stress

Words ending in a vowel (or n or s (e.g., plurals)) are stressed on the penultimate syllable:

casa, limonada, zapatos, lunes, escriben, hermanos, joven, computadora

Other words are stressed on the last syllable:

comer, estoy, español, Madrid

Diphthongs (see also pronunciation) normally combine to make a single sound/syllable with some of both sounds:

bueno, paella, tiene, hacia

The diphthongs iu and ui (both weak vowels) stress the second:

diurno, ruido

Acute accent

The acute accent is used when the stress in not as in the above:

lápiz, canción, está, túnel, café, perdó

and similarly to alter the diphthong rules (also in two vowels separated by h or in a triphthong) to stress one vowel:

canción, país, oído, prohíbe, veníais, flúido

Acute accents are also used to distinguish words that have different function or meaning that would otherwise be spelled the same; the accented vowel is stressed.

e.g.,

Adjectives/pronouns:

mi – my; mí – me

el – the; él – he

tu – your; tú – you

este – this; éste – this one

Relative pronouns/interrogative & exclamatory pronouns:

donde – where; ¿dónde? – where?

cuanto – as much as; ¿cuánto? – how much?, how!

Others:

como – as, like; cómo – how

mas – but; más – more

si – if; sí – yes

de – of, from; dé give (subjunctive 3psing)

se – ...self (pronoun); sé – I know (saber), you be (ser, imperative)

te – you (pronoun); té – tea

que – who, that, which; qué – what, how, which?

Accent rules ‘technical’ Spanish names:

• Agudas – oxytone (literally: ‘sharps’); when the final syllable of a word is stressed and it ends in a vowel, n, or s.
  e.g., café, perdón
• Llamas – paroxytone (literally: ‘flats’); when the penultimate syllable of a word is stressed and it does not end in a vowel, n, or s.
  e.g., fácil, árbol
• Esdrújulas – proparoxytone; when the antepenultimate syllable of a word is stressed (regardless of its ending).
  e.g., música, década, jóvenes

Tilde

The tilde is only used to form ñ:

mañana

Diaeresis (looks like umlaut)

The diéresis (diaeresis) is only used as ü, to indicate the u is pronounced between g and e/i (otherwise it would be silent):

lingüista – linguist

pingüino – penguin

vergüenza – shame