Cool MateI don't know it vs I'm not sure
When to use each in English, with meaning, register, and examples.
I don't know it
Top 2,000 (common)
I'm not sure
High-frequency chunk
Most common: I'm not sure
| I don't know it | I'm not sure | |
|---|---|---|
| Pronunciation | 🇬🇧 //aɪ dəʊnt nəʊ ɪt//🇺🇸 //aɪ doʊnt noʊ ɪt// | 🇬🇧 //aɪm nɒt ʃʊə//🇺🇸 //aɪm nɑt ʃʊr// |
| Meaning | I am not sure about it. | I don't know if it's true or not. |
| Example | After hearing the question, I replied, 'I don't know it.' | I'm not sure if it will rain tomorrow. |
| Register | Neutral | Neutral |
| How common | Top 2,000 (common) | High-frequency chunk |
| Collocations | don't know it well, don't know it anymore, don't know it at all | I'm not sure about that, I'm not sure if, I'm not sure what to do |
| Common mistakes | Using 'know' incorrectly with a subject (e.g. 'I don't know he')., Omitting 'it' when referring to a specific thing (e.g. 'I don't know')., Confusing with 'I don't understand' which implies confusion, not lack of knowledge. | Using it too formally in writing., Confusing it with 'I'm not certain' - which is slightly more formal., Overusing it in situations that require decisiveness. |
| Usage notes | Used to express uncertainty or lack of knowledge about a topic; appropriate in both formal and informal contexts. | Used when expressing doubt about something. Common in conversations but less formal in writing. |
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Frequently asked questions: I don't know it vs I'm not sure
What's the difference between I don't know it and I'm not sure?
I don't know it: I am not sure about it. I'm not sure: I don't know if it's true or not.
Which is more common: I don't know it and I'm not sure?
I'm not sure is the most common in everyday English.
Can you show an example of each?
I don't know it: After hearing the question, I replied, 'I don't know it.' I'm not sure: I'm not sure if it will rain tomorrow.
Can I use I don't know it and I'm not sure interchangeably?
Not always. I don't know it and I'm not sure are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.