Certain about vs Certain of

Do you wonder which one is correct?

The short answer is that both phrases are correct.

But they do not mean the same thing.

The difference is tricky, and you will make mistakes if you don’t understand it.

To learn more, read on.

 

Certain about (something)

Certain about can be extremely vague and that is why it can be used in many different contexts.

“Certain about” means you are very confident that you know something. There is no doubt in your mind that some information is correct and reliable. You strongly believe that you have the knowledge of some details or facts that relate to a particular thing.

I am certain about who it was. (= I strongly believe I know who that person is) You said delivery is due today, but are you 100% certain about this? (= are you absolutely sure it is today?) We think Leo stole the money from the cashbox, but we are not certain about our suspicions. (= we do not know that it was him) Mary says she is not certain about having children. (= she does not know whether or not she wants to have children)

Sometimes a sentence is so vague that it can have several different meanings.

I am not certain about him. (= I do not know whether or not I like him) (= I do not know if I can trust him) (= I do not know whether or not he is the right person for a particular job or responsibility) I am not certain about my role. (= I do not know what my role is) (= I do not know what I am expected to do) (= I have doubts that my role is useful) (= I doubt if I can play my role well)

 

Certain of (something)

Certain of is used when you are confident that something is true, correct, exists, or is going to happen.

Unlike “certain about”, “certain of” should never be used in vague contexts. Instead, you should only use it when talking about something specific.

I am certain of victory. (= I am confident that I will win) You must apply early to be certain of getting a place. (= to be sure that you will get it) Whether or not this idea will work out is not something I am certain of. (= I am not confident it is a good idea) ‘What time do you start?’ ‘I am not certain of the exact time.’ (= I am not confident that I know that) William is very certain of his role as leader. (= he feels confident because he believes that he is a good leader and can do it well)

 

Similarities

Sometimes the difference in meaning is small. When that is the case, you can usually use the two phrases interchangeably.

Mary says she is not certain about having children. Mary says she is not certain of having children.

You said delivery is due today, but are you 100% certain about this? You said delivery is due today, but are you 100% certain of this?

‘What time do you start?’ ‘I am not certain about the exact time.’ ‘What time do you start?’ ‘I am not certain of the exact time.’

 

Differences

Sometimes the difference is stark and you should choose one over the other.

I am certain about victory. I am certain of victory.

William is very certain about his role as leader. William is very certain of his role as leader.

There’s only one thing I am certain about: you cannot stay here. There’s only one thing I am certain of: you cannot stay here.

 

Summary

• “Certain about” is a vague phrase that can be used in a variety of situations and contexts when you think something is correct,
• “Certain of” is used when talking about something specific that you think is true, correct, exists, or is going to happen.