What Is An Illusion?
A magician is basically using the principals of many different types of illusion, which is a contradiction of perception that doesn't make sense to the viewer. An illusion as a magical effect is taking advantage of these principals and using them to their fullest extent. Everything that is needed for the trick is already accomplished and what your seeing is not what you think it is because the magician takes credit for it by making it look magical. With this as a possibility, imagine seeing a card slowly morphing into another identity or witnessing a solid object melt through another solid object.