We have already seen that the focus is on Macbeth and his wife, furthermore, we have seen that the crucial problem is the decision and the act, especially in which sense you can consciously and freely choose to do evil, then do it and then be faced with the consequences. The problem is old. Socrates maintained that no one with full insight in what was evil, would of his own free will do it and that claim had been dominating for almost two millennia. The logical power of this claim was that it was a tautology or even better; a definition.
Any human activity, to think, to speak, to act, has to focus on a purpose. The definitive impulse to throw yourself into an activity is the urge towards selfpreservation that lies deep in any living creature. That is why man cannot want his selfdestruction; he only wants the Good, understood as that which promotes its own selfpreservation.
If, however, we exclusively define the Good as man's selfpreservation, man's different attempts to achieve this would lead to mutual destruction. If I - and everyone included - unhampered and in absolute selfishness only seek my own, the misfortune I could inflict on someone would naturally be limitless. So there has to be a further addition to the concept of Good.
The Good, we might add, is not only the instantaneous need for satisfaction - in a matter of time it will often turn out to be an evil - but it is in fact the absolute purpose for any human being (the highest Good), and it isn't just common for everyone, but, when you strive for it, you include the others in a true community.
But that means that the Good isn't just a subjective phenomenon; it is objective, and in a philosophical analysis you begin to see a picture of a hierarchical construction of still higher goods, from the simple ones you can strive for in everyday life to the eternal salvation that can only be sought for its own sake. Since man wants to be in accordance with himself and since the whole area of Good is conform with man, man must freely want the Good; you could be more accurate by saying that man necessarily wants the Good.
However, it is a fact that man once in a while actually chooses the evil and that needs an explanation. First and foremost, this explanation is lack of insight. It is reason which in the given situation can choose the right possibility and then make the will act upon it. But reason can be mistaken; the situation can be confused or you can find yourself in a conflict where it is doubtful which possibility is right. Under these circumstances man can do evil in the false belief that it was the Good.
The source of error could be found in man's desire as well. We've all got our weaknesses, strong inclinations, and we know that in a certain situation we can succumb to them. As we know the near Good is a stronger impulse than the more distant Evil. If you, however, express it in rational categories, you could say that again reason is wrong. It believes it's a greater Good to satisfy the immediate inclination than - if necessary - to give it up because of a more distant Good. And you could add to it that there is a strong urge to fulfil the inclination because you identify with it; without it - and its fulfilment - you weren't yourself.
Even though we no longer express the relation in these terms philosophically, we're faced with everyday phenomena so familiar that we all know them and it's by virtue of this we're able to understand "Macbeth". Macbeth is the man who consciously and freely chooses Evil. He is the tragical figure because he looks like any of us but finds himself in an extreme situation where the act is no longer more or less harmless, but absolute in its consequences. Macbeth's act is a breach with all natural feeling and all natural duties and he knows. Once and for all he does what cannot be done, which cannot be done again or undone, which cannot be withdrawn, which isn't just a partial, maybe...