Yea, there thou mak’st me sad, and mak’st me sin 
In envy that my Lord Northumberland 
Should be the father to so blest a son, 
A son who is the theme of Honor’s tongue, 
Amongst a grove the very straightest plan, 
Who is sweet Fortune’s minion and her pride; 
Whilst I, by looking on the praise of him, 
See riot and dishonor stain the brow 
Of my young Harry. 
(Act 1, scene 1, lines 77–85)

These lines, which King Henry speaks in the first scene of the play, set the stage for the conflict between Hotspur and Prince Harry. Henry describes the fame and fortune of young Hotspur, calling him “the theme of Honor’s tongue.” In comparison, he says, Prince Harry has been sullied by “riot and dishonor.” The opposition between these two young men is thus primarily a function of honor. Honor must be earned through proper conduct and worldly achievement. It’s precisely because Hotspur has proven himself on the battlefield that Henry goes on to wish that he, and not Harry, were his son. Hotspur’s honor makes him a better candidate for the throne than the prince.

Now, by my scepter, and my soul to boot, 
He [i.e., Hotspur] hath more worthy interest to the state 
Than thou, the shadow of succession. 
For of no right, nor color like to right, 
He doth fill fields with harness in the realm, 
Turns head against the lion’s armèd jaws, 
And, being no more in debt to years than thou, 
Leads ancient lords and reverend bishops on 
To bloody battles and to bruising arms. 
(Act 3, scene 2, lines 100–108)

Act 3, scene 2, marks the turning point of the play, where King Henry confronts Harry about his dishonorable conduct. In these lines, Henry repeats a sentiment he first voiced in act 1, where he fantasized that a fairy had switched Hotspur and Harry at birth, making Hotspur his real son and heir. Here, Henry tells Harry that his rival effectively has a better claim to the throne. However, the king’s words here have nothing to do with hereditary legitimacy. Instead, Henry is pointing out that Hotspur surpasses Harry in terms of honor, which is a key element of kingliness. The Earl of Douglas will echo this idea more explicitly in the next act, where he evaluates Hotspur as “the king of honor” (4.1.10). In other words, Henry is making an oblique argument that Harry must reform himself if he wants to be honorable and hence worthy of the throne.

Honor pricks me on. Yea, but how if honor prick me off when I come on? How then? Can honor set to a leg? No. Or an arm? No. Or take away the grief of a wound? No. Honor hath no skill in surgery, then? No. What is honor? A word. What is in that word “honor”? Air. A trim reckoning. Who hath it? He that died o’ Wednesday. Doth he feel it? No. Doth he hear it? No. ’Tis insensible, then? Yea, to the dead. But will it not live with the living? No. Why? Detraction will not suffer it. Therefore, I’ll none of it. Honor is a mere scutcheon. And so ends my catechism. 
(Act 5, scene 1, lines 131–42)

Humorously countering the play’s emphasis on the importance of honor, Falstaff delivers this diatribe against honor during the Battle at Shrewsbury, just before the climax of the play. Linking honor to violence, Falstaff says that honor is useless when one is wounded: it cannot set an arm or a leg, or take away the “grief of a wound,” since it has “no skill in surgery.” In fact, being merely a word, honor is nothing but thin air—that is, the breath that one exhales while saying the word. Falstaff declares that the only people who have honor are the dead, and it does them no good, for they cannot feel or hear it. He therefore concludes that honor is worthless, “a mere scutcheon,” and that he wants nothing to do with it. In a play obsessed with the idea of honor, this speech implicitly questions the moral values on which most of the characters base their lives.