Anselm's Doctrine of Substitution

What does this have to do with the topic of "Anselm's Doctrine of Substitution"?

No.It is more a matter of definition.It may be that there is some powerful being who enjoys lying, but then this being is not God. And if this is the only being that otherwise meets Anselm's criteria for 'God', then Anselm would have to conclude that there is no God (since the being that exists does not meet all the definitional criteria).But Anselm believes there is a God, and with this comes the belief that a being exists whose character satisfies all the criteria for 'God'-ness - including the criterion against lying.And so the argument is that God cannot lie, not because there is a powerful being lacking the capability, but because no powerful being worthy the title 'God' would lie - in Anselm's opinion.Jon