Certainly you can define classes at runtime. But I think this is the wrong way to go about logical reasoning. What happens when you want to express that Socrate

Certainly you can define classes at runtime. But I think this is the wrong way to go about logical reasoning. What happens when you want to express that Socrates is a dead Greek philosopher? Do you have DeadMortal (subclass of Mortal with isDead() returning true), GreekMortal, PhilosopherMortal (subclass of UnemployedMortal)? I think you may get further if you look at a language like Prolog -- work along the lines of predicates, rules, and attributes.