Cur rent ont ologi es' upp er-le vel tax onomi c str uctur e is oft en qui te com plica ted and hard to und ersta nd. In thi s pap er I sho w how the the oret ical too ls of so- calle d For mal Ont ology , and esp ecial ly the the ory of ide ntity , can hel p to for mulat e cle aner, mor e gen eral, mor e rig orous , and mor e und ersta ndabl e upp er-le vel ontol ogies . I foc us in par ticul ar on som e exa mple s of mul tiple gen erali zatio n, pro posin g a way of sim plify ing the dom ain str uctur e by spl ittin g som e con cepts acc ordin g to dif feren t ide ntity con ditio ns, or by exc ludin g the m becau se of the ir lim ited org aniza tiona l rol e.