Reporters tried to pin him down on the specific changes he wants to make to the tax laws.记者们竭力要他说明他想对税法做出的具体改变。

He talked in a general way, but they couldn't pin him down to specifics.他笼统地谈了一下，但他们却没法使他说出具体细节。

Can you pin down when the change occurred?你能确定何时发生了变化吗？

I'm trying to pin down [=identify] the source of the problem.我正试图查明问题的根源。