Adjectives, adverbs, comparatives and superlatives

Consonant-ending nationality adjectives (francés, inglés, alemán) carry an accent in the masculine singular because the stress is on the last syllable. Adding -a for the feminine moves the stress, so the accent is dropped: francés -> francesa, inglés -> inglesa, alemán -> alemana (never francésa). Plurals lose it too: franceses, francesas.

Not every adjective behaves like rojo. -e and -ista adjectives never change for gender: una mujer optimista, never the invented optimisto; inteligente, never inteligento. -z adjectives do not add a plain -s — they change z to c: felices not felizes, capaces not capazes. Match the adjective to its own paradigm before agreeing it.

buen, gran, mal, primer and the rest shorten only directly before a masculine singular noun. Before a feminine noun use the full form (una buena amiga, not una buen amiga); before a plural, the full plural (buenos amigos, not buens amigos). Note gran also shifts meaning: una gran mujer = a great woman, una mujer grande = a big woman.

Two false beliefs cause errors. First, "all adjectives change like rojo" — but only -o adjectives have four forms; -e and -ista never change for gender (optimisto is invented). Second, "buen, gran, mal go anywhere" — valid only before a masculine singular noun; before feminine or plural use the full form (buena amiga, buenos amigos).

The commonest accuracy error is writing the dictionary (masculine singular) form regardless of the noun: los ojos azul instead of azules; ella es bajo instead of baja (ella is feminine); and the invented azuls (the plural of azul is azules). Check every adjective against the noun's real gender AND number, not on autopilot.

Number agreement covers the verb too, not just the adjective. A plural subject needs the plural ser: son más interesantes, not es más interesantes. Likewise a 3rd-singular es used with an actually-plural subject is flagged every sitting. Re-check: does the subject match in number with both the verb and the adjective describing it?