Could anybody explain the difference between preliminary and provisional?
Before the trial against people who do not use the internet to check something for themselves can start, there has to be a preliminary investigation to establish who the culprits are. (preliminary = preparatory, introductory)
This is not a provisional answer. It is the one and only you will get from me. Provisional = temporary, for the time being.
I think in some limited contexts, the two words could be used interchangably. Look at the two definitions on Dictionary.com:
There is some weak overlap between the words, but they don’t in general have the same meaning. Anyway, SanneT already explained what they mean.