Why different failure criterions when one can be related with the other?

Hi all,
I have a basic question (and cud be a stupid one too :). Why we have an energy criterion for fracture? When we can always derive energy from stress and strain (or stress and young's modulus or strain,stiffness and displcement) ... How a energy criterion basically differs from stress and strain criterion? .. As far as i read it is said energy criterion shud be used when plasticity comes into picture .... but still in the plastic region plastic stress and plastic strain have unique relation then why again we bother about ENERGY? ... Won't it be sufficient to have a stress based or strain based criterion? .. again i wonder why there is even stress and strain based criterion ! as they can be related directly through some material constant. It could be a stupid question kindly experts in this area help me get it cleared. Thanks.