seriously doubt — not believe
collocationB2IELTS 5.5+neutralcommon
To strongly think that something is not true or will not happen.
Say it like a native
Textbook I harbour grave reservations as to whether he will appear.
Native I seriously doubt he'll show up.
Natural; 'harbour grave reservations' is formal/legalistic.
Pattern: seriously doubt + (that) clause / noun phrase
In use
- I seriously doubt he will finish the project on time.communication
- To be honest, I seriously doubt that most people recycle as much as they should, even though they know it's important.IELTS speaking
Common mistake
✗ I seriously doubt that he will not come.
✓ I seriously doubt he'll come. (= I don't think he will)
'Doubt' already means 'don't believe' — don't add a second negative.
Common collocations
seriously doubt— whether, that, I, very much
Don't confuse it
'Doubt' alone is weaker; 'seriously doubt' is much stronger and more certain.