对某事表示确定的表达用词
这些词用来形容某人知道某事是准确的、真实的或将要发生的。
“Certain”是最常用的词汇之一。它通常用在动词后面，可以和absolutely、completely这样的词连用来强调。
I feel certain that this change will be for the best.
Are you absolutely certain you switched off the iron?
How much will it cost? I'm not certain.
确定certain的反义词是Uncertain （不确定）。Uncertain主要用于写作，比确定更正式。它用来描述人们对一件事不确定，或者某件事不确定或不确定。
The economic outlook is still uncertain.
The press secretary said she was uncertain whether troops would be deployed.
短语know for certain或say for certain也可以指知道某事是准确的或真实的。它们常用于否定陈述中。
I can't say for certain, but I think he's coming to the party.
What will the future bring? No one can know for certain.
We know for certain that she's planning on leaving her job – she told us.
另一个表示毫无疑问地知道某事准确或真实的常用词汇是sure。Sure是一个比certain更简单的词，但它有非常相似的用法。Sure也可以用在动词后。
Don't worry – I'm sure it won't be a problem.
Are you sure about that?
sure的反义词是Unsure。“Unsure”比“sur”更正式。
He's unsure of whether or not he'll be able to join us.
Detectives are unsure about the criminal's motives.
如果你说你很Positive肯定某事是真的，你是在强调你知道它是真的。Positive用在be动词后面。
"Are you sure you let the cat in?" "I'm positive."
有很多习语可以用来表示你确定某事是准确的或真实的。你可以说你对它很确定you are sure of it，或者某事是肯定的for sure.。
He's the one who stole my bike – I'm sure of it!
One thing's for sure: I'll never go on a date with her again.
I know for sure that he posted the cheque last week.
如果你对某事非常确定，你可以用“beyond a shadow of a doubt”这个习语来形容你有多确定。你也可以用You can bet your life这个短语。这两个短语都很强调语气。
It has been proved beyond a shadow of a doubt that the medication is effective.
I know beyond a shadow of a doubt that he's innocent of the crime.
He's such a careful writer, you can bet your life that every single detail is thoroughly researched.
如果你非常确定你要说的事情的准确性，你可以在陈述之前使用这个短语it's safe to say (that)。
I think it's safe to say that he will win a majority of votes.
We've waited for almost an hour – it's safe to say she's not coming.
当你非常确定某事会发生或某事是真的时，你可以使用no doubt这个短语。
You will no doubt want to see the evidence.
No doubt she's running late, as usual.
如果你注定要做某事，你肯定会做这件事或者它会发生。Bound通常后跟to和不定式。在英式英语中，你也可以用I'll be bound这个短语来表示你对某事很确定。这个短语已经过时了，但仍然出现在口语中。
He's bound to have the spare parts around.
UK: He's on holiday, I'll be bound.
如果你对某事有信心，那就意味着你相信那件事，所以确信它会发生。“Confident”是一个非常强调的词，通常用在be动词后面。
I am confident that doctors will find a cure.
如果你确信某事convinced of ，你确信它是真的基于你所看到或相信的事情。
Police are convinced they have the right suspect in custody.
He's been lying to me – I'm convinced of it!
