infer
Infer is to reach an opinion or decide that sth is true on the basis of information that is available. Because A then B.
"Infer"是根据现有的信息得出一个意见或决定某事物是真的。因为A所以B。
- I infer from your question that you are not a native English speaker.我从你的问题中推断出你不是以英语为母语的人。
- I inferred from what she said that you have not been well.我从她的话语里推断你一直不太好。
- Like this certainly helps us to infer molecular mechanisms. 这样的能帮助我们推断,一些分子机制。

speculate
Speculate is to form an opinion about sth without knowing all the details or facts,or to form a theory about a subject without firm evidence.
"speculate"是在不知道全部细节或事实的情况下对某事物形成一种看法,或在没有确凿证据的情况下形成某种理论。
- It's always hard to speculate about the future.未来一向很难预测。
- I can speculate who will win the football game tonight.(Based on the teams playing, their past performance, whether it's a home or away game, etc).我可以推测今晚谁将赢得这场足球赛。(根据参赛球队,他们过去的表现,无论是主场还是客场比赛,等等)
- The doctors speculate that he died of a cerebral haemorrhage caused by a blow on the head.医生推测他死于头部受击引起的脑溢血。

总结:从他们的释义来看,因为他们推测的依据存在区别,所以"Infer"做出的推断可能要比"speculate"更加接近事实。
练习:(下面这个空你认为应该填哪一个更好呢?把你的答案写在评论区一起讨论吧!)
It can be ________ from the passage that wearing seat belts will get drivers out of dangerous situations.