快速答案
mas 表示转折；mais 表示增加或更多。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
mas
but
Use mas for contrasting one statement with another.
mais
more or plus
Use mais for a larger amount, addition, or comparison.
如何选择
- mas: Choose mas if the sentence points to contrasting one statement with another.
- mais: Choose mais if the sentence points to a larger amount, addition, or comparison.
例句
Quero ir, mas estou cansado.
I want to go, but I am tired.
Quero mais café.
I want more coffee.
常见误区
They sound very similar in much of Brazil. Replace mas with porém or mais with menos to test the meaning.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 mas，一次用 mais。如果两个版本都可以，说明意思怎样变化。