Gary,  Look for the "Inspect Task" command (in the "Tasks" block of the Task Ribbon), which opens the Task Inspector pane.  The "Predecessors" listed by the Task Inspector are the driving predecessors for the selected/active task.  Each driving predecessor is provided as a hyperlink, so you can use it to jump back from task to task through the driving logic path.  These calculations are independent from the "Critical" flag; you can trace the driving logic path for any task regardless of its criticality.  For MSP 2013 and later versions, also look for the "Driving Predecessors" bar style on the Task Path menu of the Format Ribbon.  That bar style graphically depicts the same trace.  That's the good news.   The bad news is that MSP's internal calculations of driving logic can be quite wrong under many real-world conditions - (Problems with Driving Logic in Task Inspector and Task Paths (Microsoft Project 2010-2016)).  During crashing exercises, these can lead to a focus on shortening tasks that ultimately have no impact on the project completion date.  Besides computing drag, the BPC Logic Filter add-in that Steve mentions includes its own Task Logic Inspector that offsets these issues and provides a bit more functionality.  Good luck, tom