Grammar fix
a vested interest
personal stake (often hidden or self-serving)
a strong personal reason for wanting something to happen, especially because you will get an advantage or benefit from it, sometimes at the expense of others.
Hear it in context
Notice where the phrase sounds natural.
- The committee members all have a vested interest in the outcome of the decision.work
- In my opinion, when politicians have a vested interest in certain industries, it can lead to biased decisions that do not benefit the public as a whole.IELTS speaking
Fix the pattern
Pattern: have a vested interest (in something)
WrongHe has a vested interest on the deal.
RightHe has a vested interest in the deal.
'A vested interest IN something', not 'on'.
Patternhave a vested interest (in something)
Use it right
Choose the version that sounds natural in speech.
'Pecuniary interest' is legalese; 'a vested interest in' is the natural idiom.
Build natural chunks
Words that usually travel with it.
a vested interest ininhavesuchthose with
Don't confuse it
Unlike the general word 'interest', 'a vested interest' implies a personal benefit or hidden motive, not just curiosity or involvement.