bom/boa/mau/má

In Portuguese, adjectives match the noun in gender and number. Bom and mau are common but have specific irregularities.

1. The Forms of 'Good':

• Masculine Singular: bom
• Feminine Singular: boa (the nasal sound in 'bom' disappears)
• Plurals: bons and boas (Note: bons follows the standard rule of changing -m to -ns)

2. The Forms of 'Bad':

• Masculine Singular: mau
• Feminine Singular: má (requires an accent because Portuguese spelling rules dictate that stressed monosyllables ending in A, E, or O must be accented)
• Plurals: maus and más (Note: maus follows the standard rule of adding -s to words ending in -u)
• Note: The word ruim is a very common alternative for mau. It is invariable in gender (e.g., um filme ruim, uma ideia ruim) and its plural is ruins. In Brazil, mau is often reserved for moral character (e.g., um homem mau - a wicked man), while ruim is used for poor quality or bad health (e.g., comida ruim - bad food). However, mau is still used in Brazil in several very common fixed expressions where 'ruim' cannot be used, such as mau humor (bad mood), mau hálito (bad breath), and mau perdedor (sore loser). Ruim is also used in Portugal, though mau is more frequent there for general use.

3. Irregular Comparatives and Relative Superlatives:
Instead of saying 'mais bom' or 'mais mau', these adjectives usually use unique forms to compare things:

• melhor (better) / Plural: melhores
• pior (worse) / Plural: piores

These comparative forms are invariable in gender, meaning they are the same for both masculine and feminine nouns (e.g., o melhor livro, a melhor casa).

To say 'the best' or 'the worst' (relative superlatives), simply add the definite article before the comparative: o/a melhor (the best) and o/a pior (the worst).

Note: You can use 'mais bom' or 'mais mau' only when comparing two qualities of the same person or thing (e.g., Ele é mais bom do que inteligente - He is more good than he is smart).

4. Absolute Superlatives:
To express 'very good' or 'very bad', Portuguese frequently uses these synthetic absolute superlatives:

• ótimo (great/excellent)
• péssimo (terrible/awful)

These act as regular adjectives and change for gender and number (e.g., ótimos, péssimas).

5. Word Order:
These adjectives often come before the noun when expressing a subjective opinion (e.g., um bom amigo). Placing them after the noun can add emphasis or a more literal/moral meaning (e.g., um homem mau - a wicked man).

6. Adjective vs. Adverb:
Do not confuse these with their corresponding adverbs:

• Bom/Boa (Adjective) vs. Bem (Adverb - 'well')
• Mau/Má (Adjective) vs. Mal (Adverb - 'badly' or Noun - 'evil/illness'). Note that the plural of the adjective mau is maus, while the plural of the noun mal is males.

Helpful Mnemonic: Bom is the opposite of Mau (both use rounded vowels O/U), while Bem is the opposite of Mal (both use E and a consonant). Also, remember that the adverbs bem and mal are invariable (they do not change for gender or number).