1. Perhaps/maybe
These two words are used for saying that you are not certain about something, or that something may or may not be true.
这两个词可以用在你对某事不确定的情况下，或是表达某事可能是真的也可能是假的。
Perhaps is more formal and is used in writing while maybe is used more in spoken English
“perhaps”更加正式，常用在写作中，而“maybe”更多用在口语中。
e.g. I wondered if perhaps he had changed his mind about attending the party.
例句：我在想关于参加派对这件事，他是不是改变主意了。
e.g. ‘When can you give me an answer?’ ‘I don’t know. Maybe tomorrow.’
例句：“你什么时候能给我答复？” “不知道，也许明天吧。”

2. Probably/possibly
These two words can confuse even native speakers. Probably is used for saying that something is likely to be true, and possibly that it may be true but you are not certain.
这两个词非常容易混淆。“Probably”用来表达某件事很可能是真的，“possibly”则表示这件事可能是真的，但你并不确定。
e.g. If house prices are low, it’s probably because there is a lack of demand.
例句：如果房价很低，那么很可能是因为需求少。
e.g. ‘Would you consider moving to another country for your work?’ ‘Possibly, I’m not sure.’
例句：“你会因为工作原因考虑移居其他国家吗？”“可能吧，我不确定。”

3. Apparently
It is used when what you are saying is based on what you have heard, not on what you know is true and therefore fact.
当你听说了某件事而不是你自己确定这件事是真的的时候，你可以用“apparently”来表示这件事是事实。
e.g. Apparently, she resigned because she had an argument with her boss.
例句：显然，她辞职是因为和老板吵了一架。
e.g. There is, apparently, going to be an announcement about the new CEO tomorrow.
例句：显然，明天就会有新总裁的通知了。

4. As far as I know/ as far as I am aware
These two expressions are used when you have partial (incomplete) knowledge of an issue or fact.
如果你对某个问题了解得不是很全面，就可以用这个词。
e.g. No one has complained, as far as I know.
例句：就我所知，没有人抱怨。
e.g. As far as I am aware, the invitations to the party have all been sent.
例句：就我所知，派对的邀请函已经全部发出了。

5. To the best of my knowledge
This phrase is used for saying that you think something is true, but you are not completely certain. This is quite a formal expression.
当你认为某事是真的，但又不确定的时候可以用这句话。
e.g. To the best of my knowledge, no similar book has been published.
例句：就我看来，还没有类似的书出版过。

6. Not to my knowledge
This is used for saying that you think something is not true, although you are not completely certain.
当你认为某事不是真的，但又不确定的时候可以用这句话。
e.g. ‘Has the report been sent yet?’ ‘Not to my knowledge.’
例句：“报告交上去了吗？” “我觉得没有吧。”

7. I imagine/suppose/guess
These are used when you think something is probably true, but you can’t be sure. “Guess” is more frequently used in American English, although you can hear it in British English, too. “Suppose” is more characteristic of British English and is often used in the negative.
这些词可以用在当你认为某事可能是真的，但又不确定的时候。“guess”更多地出现在美式英语中，尽管也有英国人会用。但是“suppose”是更加地道的英式英语，而且经常用在否定句中。
e.g. I imagine they’ve already left for the airport.
例句：我认为他们已经离开机场了。
e.g. I suppose she must be delighted about getting the job.
例句：我认为她得到这份工作一定很开心。
e.g. I guess he will want to meet all the team members before the conference.
例句：我猜他想在会议前和团队成员见面。