Selection.Flags (Word)

Returns or sets properties of the selection. Possible return values are wdSelActive - The selection is the active selection, wdSelAtEOL - The selection is at the end of the letter, wdSelOvertype - The selection was overtyped, wdSelReplace - The selection was replaced, wdSelStartActive - The selection is at the start of the active document.

ActiveDocument.Words(1).Select 
MsgBox Selection.StartIsActive 
Selection.Flags = wdSelStartActive 
MsgBox Selection.StartIsActive