Shakespeare gives the reader the opportunity to view the timeless duplicity of a politician in Prince Hal of Henry IV, Part 1. Instead of presenting a rather common hero, Shakespeare sharpens the both sides of the sword and makes Hal a deceitful prince. In order to portray accurately the treachery and fickleness of Hal, Shakespeare must provide Hal with models to follow, rivals to defeat, and a populace to convince. Although Hal would not have to grovel for votes from England's populace to become king, he does understand the problems of being an unpopular ruler from witnessing his father's problems.
So Hal needs to persuade a general population that he is competent in order to remain a king once he has obtained the throne. Shakespeare wants the play to seem sympathetic to Hal, and he wants Hal to convince the audience (populace) himself. Therefore, Hal's fraudulence is hidden in undertones and slips of the tongue which he makes throughout the play. The first indication of this comes at his soliloquy in Act 2, Scene 1. It would be impossible for a reasonable man to have boozed and bummed all of his teen years and suddenly renounce his life and become reborn. There is an amoral quality to Hal that allows him to change allegiances as political winds would call it wise.
But it is not just amorality that makes Hal a politician - he desires power as well. His amorality culminates in his eulogies for Hotspur and Falstaff with the greatest grasp of power he makes in the play. After he gives them and Falstaff is found alive, he realizes that he has made a slight blunder and backs off a bit, allowing Falstaff some room to remain. But while he delivers them, he is at his best, being the worst. His basic behavior appears king-like, but the subtleties show his utter disregard for those who love him and his calculating mind making political estimates so that he can secure the throne. Even though Hal is an amoral huckster, he must be able to convince others of his worthiness for the play to work.
Therefore, Shakespeare must spend most of Hal's speeches using a convincing tone. He will use the overtones and most of the direct meanings of what Hal says to convey a thoughtful prince; he will use the undertones and occasional slips to give insight to the reality of Hal's persona. In order to understand fully why Hal's eulogies are a culmination of his quest for power, one must examine how he uses them to gain favor from the public. After killing Hotspur, a respected rival, Prince Hal closes the chapter on him elegantly. He starts by finishing the sentence that Hotspur began, and philosophizes a bit about the deadly sin that did him in: A kingdom for [your ambition] was too small a bound, But now two paces of the vilest earth Is room enough. Hal clearly shows his countrymen that he knows greed is bad, and to look out for what happens if one gets too gluttonous.
It is the speech of royalty, carefully phrased and in iambic pentameter. Hal has clearly come into his own here, and delivers a chastising almost worthy of a king. Then he continues, praising Hotspur for his virtues, for it is important to pay homage to duties done for the king. And finally, Hal promises not to 'remember' Hotspur's treason. (V: 4: 103) Of Falstaff, Hal has little to say.
Because he has 'reformed' his ways, Falstaff ranks only as an 'old acquaintance.' (V: 4: 104) Hal reluctantly acknowledges that he would have grieved for Falstaff - 'I should have a heavy miss of thee / If I were much in love with vanity' - if he had not reformed. (V: 4: 107) Hal takes Falstaff's death in course, accepts it, and moves on. He is now a Prince, and it seems like his thoughts and actions are on high. But Hal's thoughts aren't on high moral ground. He's a manipulative man whose only goal is power. If he really had respect for Hotspur, his first line in eulogy would not be referencing Percy's digestion by worms.
If Hal cared for homage, he would not feel the need to cry triumphantly, 'How much art thou shrunk!' which cannot be construed as anything but a disturbing view into Hal's immediate emotion. (V: 4: 90) He's gleeful because now he is the only son remaining. He has risen to power, and crushed Hotspur soundly. After this slip, he rights himself and tempers his message a bit, to make it a general condemnation of the sin, not the sinner. But again, after he pauses and covers Hotspur's face, the first thing out of his mouth is how this act he's putting on for the benefit of his audience will assist him in his power mongering.
'I'll thank myself / For doing these fair rites of tenderness.' (V: 4: 99-100) Hal is constantly aware of what he's doing and saying and the political effect it will have. And again, immediately after we see briefly inside his head, Hal leaps back to his false veneer and continues his gentle chiding. But the duplicity is evident. Shakespeare gives us the global picture (Hotspur has just been killed, and Hal celebrates his decomposition), the undertone (continual scolding of Hotspur), and little slips from Hal about what he's really thinking. After he has killed his main rival, Hal can feel the throne within his grasp, and cannot contain the sleazy politician beneath. Still, there is an even clearer example of Hal's amorality in his words to Falstaff.
Falstaff and Hal are old friends, and Hal rewards Falstaff throughout the play, despite his incompetence. Thus, Hal's condemnation of Falstaff in his eulogy appears extremely harsh. But Shakespeare has clearly painted Hal the malevolent, and there is no ambiguity about Hal's motives. To fully understand the situation that surrounds Falstaff's eulogy, we have to consider Hal's appointment of Falstaff to military leader. Hal knows Falstaff at this point - any amount of thought would clearly rule out Falstaff as a competent general.
And if Hal is truly king material, then he must think about all-important decisions. So he chooses Falstaff on purpose, even though he realizes Falstaff will assemble a pathetic army. But there are only two reasons that would drive Hal to hire Falstaff in this capacity. He wants Falstaff out of his life forever - and it's clear Falstaff is not going without a fight. Thus to expose him as hopelessly inept would give Hal an excuse.
And secondly, Hal might need someone who looks bad to make Hal look good. Both of these reasons are absolutely horrible for a friend to do to a friend. So it's clear coming into the battle that Hal has no great love for a man with whom he has spent many years, and that his motives are far from pure. The division widens at Falstaff's [supposed] death. Hal finally feels free to express his relief at no longer having to worry about Falstaff. Again, his first words are to completely lapse, jabbing at Falstaff's weight.
But he does not recover as well here as he did with Hotspur, and continues to show how little he cares for his supposed friend. 'Death has not struck so fat a deer today, / Though many dearer in this bloody fray.' (V: 4: 109-110) So not only is Falstaff the fattest man in battle, but he's also fairly worthless to Hal and his cause. There are no mentions of the happy pasts that Hal shared with him. It's cold, hard politics, and Hal cuts him free in front of his populace. But not without making it unequivocally clear that he really feels nothing for friends: he closes his eulogy by comparing the wretched Falstaff unfavorably with his despised rival, Hotspur.
No noble man would treat an old friend the way Hal does, and in this way we know that Hal is a duplicitous prince. This two-faced ness of Hal is Shakespeare's triumph in Henry IV, Part 1. He must appease the audience by making Hal a believable character who rises from the depths of society. But Shakespeare realizes that there is no way Hal could rise the way he does without being a scheming bastard. So he uses undertones and slips of the tongue to show the element that drives Hal is not some abstract sort of kingly goodness, but rather raw power, unencumbered with morals.
Hal is not a noble son of a king, but rather a Machiavellian Prince.