我想要把这房子卖掉，买一栋小一点的，我有这想法已有一段时间了，但不肯定。

I think I shall sell this house and buy a smaller one, I have had it at the back of my mind for some time.

youdao

在不肯定的时候，使用简单而文法正确的句子来传达正确的信息比用文法复杂但不正确的句子传达错误的信息更有效。

When in doubt, it is best to use simple but grammatical correct sentences that convey the correct idea then complicated grammatical incorrect sentences that convey the wrong idea.

youdao

But, it doesn't always work because you have to be damn sure you're right.

但此方法也不经常奏效因为你必须得,十分肯定你的做法是正确的。

耶鲁公开课 - 金融市场课程节选

He wants you to finish everything by tomorrow, but you think it's impossible.

他想让你在明天之前把所有事都做完，但你觉得这肯定是不可能的。

How can I 课堂 - SpeakingMax英语口语达人

They affirm some personal rights for the slave, but not all.

他们肯定奴隶有一些人权，但不具备全部的。

耶鲁公开课 - 旧约导论课程节选