To reason or to discuss earnestly, typically to point out an inappropriate behavior: “The parents attempted to expostulate with their children about the broken window.”
postulate (PAHS chuh layt”)
To assume that something is true: “The teacher stated he would postulate that the garden would do well if it rained frequently.”
It seemed silly to try to expostulate with the small children just because I had decided to postulate that perhaps they did break the window.