快速答案
conjetura 是根据不完整迹象提出的推测；especulação 更自由地探索未经证实的可能。
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
conjetura
conjecture
Use conjetura for a reasoned possibility built from incomplete signs or evidence.
especulação
speculation
Use especulação for exploration beyond confirmed evidence, or financial trading based on expected price changes.
如何选择
- conjetura: Choose conjetura if the sentence points to a reasoned possibility built from incomplete signs or evidence.
- especulação: Choose especulação if the sentence points to exploration beyond confirmed evidence, or financial trading based on expected price changes.
例句
A explicação ainda é uma conjetura.
The explanation is still a conjecture.
A notícia gerou especulação sobre a venda da empresa.
The news generated speculation about the sale of the company.
常见误区
Neither word means proven fact. Conjetura often sounds like one candidate explanation; especulação can name a wider cloud of possibilities.
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 conjetura，一次用 especulação。如果两个版本都可以，说明意思怎样变化。