These two pairs of words are very similar, but they’re not interchangeable.
Good and bad are adjectives, which modify nouns (people / places / things). In Portuguese, adjectives must agree with the noun in gender and number:
bom good masc. sing. bonsgood masc. plur.
boa good fem. sing. boasgood fem. plur.
mau bad masc. sing. mausbad masc. plur.
má bad fem. sing. más bad fem. plur.
Which One Do I Use?
Let’s look at these examples to illustrate the difference between bom/boa (adjective) and bem (adverb).
Este telemóvel é bom. Funciona muito bem.This cell phone is good. It works very well.
Notice how bom (adjective) modifies telemóvel (noun), while bem (adverb) modifies funciona (verb).Que boa menina, tão bem educada! What a good girl, so well mannered!
Here, boa (feminine form of bom) is modifying menina (noun), while bem is modifying educada (adjective). The adverb bem could never be paired with the noun in this sentence.
If you’re not sure which of the pairs fit in a sentence, look at the surrounding words and see whether the word describes a noun, verb, adjective, or adverb.
- If the word will modify a noun, use a form of bom or mau, modified to match the gender and number of the noun.
- If the word will modify a verb, adjective, or adverb, use bem or mal.
Keep in mind that if it’s easy for you to use bom/boa and bem correctly, but mau/má and mal give you a hard time, you can try mentally swapping the word for its opposite – in this case, bom or bem – to see which works. Then you can have a better idea of whether mau/má or mal would be appropriate.
Here’s one last example: