
The Constable functions as the play's clearest embodiment of French military competence undone by overconfidence — his casual pre-battle boasting with the Dauphin sets up Agincourt's catastrophic reversal with the maximum possible irony.
The Constable of France is the most capable and clear-eyed of the French commanders, and it is precisely his competence that makes his overconfidence before Agincourt so pointed a piece of dramatic irony. He shares in the general French contempt for Henry as a callow, tennis-ball-mocked upstart, trading boasts with the Dauphin and other nobles about the superiority of French horses and French valor on the eve of a battle he expects to be a formality rather than a contest.
His exchanges with the Dauphin in the French camp — competitive, faintly absurd banter about whose horse is finer, delivered hours before men will die by the thousand — capture the play's critique of chivalric bravado at its sharpest: real martial competence dressed in a self-regard that has stopped taking the actual enemy seriously. The Constable is not a fool, which is what makes the coming defeat land as tragedy rather than mere comeuppance; he simply cannot imagine that Henry's exhausted, outnumbered army poses a genuine threat.
The battle proves him wrong in the most total way the play allows: the French nobility, the Constable presumably among them, are annihilated at Agincourt while English losses are reported as almost impossibly light. Shakespeare does not give the Constable a death scene, only the silence of his absence from the play's final act — the most professionally serious voice in the French camp, undone along with the confidence he embodied.
The Constable is motivated by professional pride in French military superiority and a genuine, if ultimately catastrophic, underestimation of Henry's army — he wants the coming battle to confirm what he already believes about the relative worth of the two sides.
The Constable's competence is real — he is the most professionally serious voice among the French nobility — which makes his dismissiveness toward Henry's exhausted army all the more damning in hindsight. His banter with the Dauphin about horses and honour on the eve of battle reveals a man for whom the coming fight is still, on some level, a matter of aristocratic sport rather than existential danger.