快速答案
比较巴西葡萄牙语中的 necessario vs. indispensavel：何时使用每个词，以及要避免的常见错误。
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
necessario
necessary
Use necessario for needed, required, or useful for a goal.
indispensavel
indispensable
Use indispensavel for so necessary that you cannot do without it.
如何选择
- necessario: Choose necessario if the sentence points to needed, required, or useful for a goal.
- indispensavel: Choose indispensavel if the sentence points to so necessary that you cannot do without it.
例句
E necessario preencher o formulario.
It is necessary to fill out the form.
O treinamento e indispensavel.
The training is indispensable.
常见误区
Indispensavel is stronger than necessario and should be used when there is no real substitute.
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 necessario，一次用 indispensavel。如果两个版本都可以，说明意思怎样变化。