. Here in Act 4, after the apparitions are presented to him, he begins to act impulsively, seeming not to consult his own reason.
His order to murder Macduff's family is the first impulsive act he takes. Do you think that if he'd stopped and really considered possible outcomes that he would have decided against this action or do you think that he would have killed Macduff's family anyway? Explain.
I agree with shaketeach. Macbeth oversteps his wife's plan early on, and his killing of the guards is a surprise to her--and probably even to him. In terms of impulsive behavior, Macbeth seems to display that even earlier, when he kind of "flip-flops" over whether to kill Duncan or not. He is fairly resolute at one point, then he impulsively changes his mind again. I know he also has the pressure from his wife, but he is a military leader and presumably knows how to make a decision and stand by it. He doesn't do so here.
It must be understood, that Macbeth begins to act without the counsel of Lady Macbeth much earlier.
When he kills the grooms in Act II,scene 3, he is acting on his own.
When he planned and carried out the murder of his good friend Banquo, he is acting alone. He even tells his wife that once she knows what he has done, she will be very proud of him.
It is one thing to kill in battle and Macbeth has become quite proficient at it. Premeditated murder is something else again. He knows if he kills Duncan, he will die a bloody death. Once he has unlimited power, he can literally do whatever he wants to whomever he wants and if the Macduff family stands in his way, or he perceives them as a threat, they are gone. He has the power and the power has gone to his head.
Once he killed the king, he was condemned. There was no redemption and he knew it.
I agree that Macbeth's decision to have Macduff's family murdered is not the first impulsive action that he has taken, and he does probably use some reasoning to make the decision because the witches have warned him to beware Macduff. But Macbeth does not fully consider the consequences of having Macduff's family murdered, and he likely has not foreseen that this murder would push Lady Macbeth over the edge. She feels particularly distraught over the death of Lady Macduff, and the death is one of the things that drives Lady Macbeth to commit suicide. Had Macbeth considered that his actions might have had consequences so close to home, he may have not had the family murdered, but he certainly would have found another way to try to prevent Macduff from interfering with his position. In other words, Macbeth's intentions likely would have remained the same even if his actions were different.
First, concerning Macbeth, his ordering the murders of Macduff's family is not the first impulsive act Macbeth makes. His first impulsive act is killing the grooms that sleep outside of King Duncan's chambers. This was a variation of the plan devised by his wife, and was definitely a mistake. This impulsive act casts suspicion on him and leads to Macduff's rebellion against Macbeth.
It is at this point that Macbeth begins to act alone, without the counsel of his wife. He shuts her out of his decision-making from this point on.
Wondering whether or not Macbeth would have decided not to kill Macduff's family if he would have stopped to think about it is really beside the point. He doesn't. One can examine the difference between impulse and reason while looking at this question, but there is no way one can ever know for sure. It's pure speculation.
The witches give Macbeth mixed messages in Act 4.1. They tell him he cannot be defeated by anyone born of woman and until Birnam word moves toward his castle, but they also tell him to beware of Macduff. Macbeth decides to act on the beware Macduff warning. Macbeth is a violent man, and violence, if you will, is his default, what he turns to under pressure. His decisions that involve violence determine his success or failure.
He turns to violence when he kills the grooms without his wife's agreement, and again after he visits the witches in Act 4.1. Certainly, had he stopped to think about the decision and put it off he may have changed his mind. But then he wouldn't be Macbeth.
I will express my very personal opinion about the issue. First of all, Macbeth's gradual distancing from Lady Macbeth and not listening to her instructions anymore is a signal of Macbeth's evil maturation and autonomy. It is an ironic lesson for Lady Macbeth who wanted to prove her importance to her husband by mastering him into the deed that would make a king out of him. On the contrary the deed and Macbeth's crowning created a further gap between the two.
Mabeth as a character is exemplary for the moral directions his thinking generally takes, e.g. his reasoning whether he should kill Duncan or not in act 1, scene 7. It only starts to dip or even disappear at the time of ordering to kill Macduff's family. Macbeth's sense of moral reason deserts him only to return for one last time immediately after the death of Lady Macbeth, in his anagnorisis speech of 'tomorrow and tomorrow'.