Taylor Rule 1993 - the original definition by John Taylor with a π = a y = 0.5 {\displaystyle a_{\pi }=a_{y}=0.5} Taylor Rule 1999 - adapted and updated by John Taylor in a new research paper: a π = 0.5 , a y ≥ 0 {\displaystyle a_{\pi }=0.5,a_{y}\geq 0}