Object methods - memory usage?

Hello! Ok, this is probably a very stupid question for someone who knows how these things work internally - but I don't, therefore I ask. :) When I instantiate an object, do the methods get instantiated as well? The question is asked memory-wise, not functionality-wise. More to the point, if I instantiate many identical objects with no class variables of their own but with many methods, will I get memory used up for the methods? If I were to guess, I'd say no extra memory is used for the methods since I don't think you can dynamically redefine class methods, so there would be no reason for duplicating them instead of simply referencing the class definition - but then again, I don't know how PHP works internally... Thank you! Bogdan