>może ktoś się pomylił. Raczej nie bo w oxfordzkim jest niemal identyczne zdanie tak samo tłumaczone - I have reason to believe... mam powody przypuszczać, że...
Tu są zdanka z "reason" policzalnym (z tymi COLLOCATIONS). Powoli zaczynam to chyba łapać ale jeszcze nie do końca :)
reason
1 cause [countable] - why someone decides to do something, or the cause or explanation for something that happens
The reason I called was to ask about the plans for Saturday.
We'd like to know the reason why she didn't accept the job.
People give different reasons for wanting to change jobs.
They must have had a good reason to do it.
reason behind
He explained the reasons behind the decision.
He wouldn't give the reasons for his decision.
For some reason or other, he couldn't come today.
She wants to change her job for purely personal reasons.
I kept the photos for sentimental reasons.
She didn't answer for the simple reason that she couldn't think of anything to say.
For obvious reasons, we've changed the names.
The tower is closed for reasons of safety.
For reasons best known to herself, she's sold the house and left the country.
There's no reason whatsoever to doubt her story.
'Why did you tell him?' 'Oh, I had my reasons.'
I see no reason why it shouldn't work.