In Shakespeare's Hamlet, Hamlet and Laertes are each young men who lose their beloved fathers, however each reacts in a very different way.
In Act One, Hamlet learns that the ghost of Old Hamlet (his father) is walking the battlements at night. Though Horatio and Marcellus warn him not to pursue the apparition, Hamlet is determined, ready to kill anyone that stands in his way.
Unhand me, gentlemen.
By heaven, I'll make a ghost of him that lets me. (I.iv.93-94)
In the next scene, the Ghost tells Hamlet how horrible his present existence is. He reveals his identity to his son and then describes how he suffers in purgatory for the sins that were resting on his soul when he died.
I am thy father's spirit,
Doom'd for a certain term to walk the night,
And for the day confined to fast in fires,
Till the foul crimes done in my days of nature
Are burnt and purged away. (I.v.13-17)
The Ghost cries out to Hamlet to avenge his murder:
If thou didst ever thy dear father love—
… Revenge his foul and most unnatural murder. (29)
Up until this time, everyone believed that Old Hamlet had been bitten by a poisonous snake while napping in the orchard. The Ghost discloses that he was actually murdered by "the serpent…that / Now wears [his father's] crown." (45) This refers to Hamlet's uncle, Claudius.
Hamlet promises to avenge his father's death. Among critics there is a great deal of discussion with regard to how long it takes for Hamlet to act. Hamlet's tragic flaw is considered his indecision: that had he killed Claudius while he was praying, the play would have ended much differently.
However, there is good reason for Hamlet to hesitate. Shakespeare's Elizabethan audience believed that the devil did his utmost to win souls to their eternal damnation. The people would have sympathized with the young prince because if the Ghost was not his father but an evil spirit, Hamlet could lose his soul forever because it was considered a mortal sin to commit regicide. So Hamlet decides to watch everyone around him and look for proof of the King's guilt. He even suspects his mother Gertrude may be complicit in the act, for she hastily married her brother-in-law soon after Old Hamlet's death. Ultimately, Hamlet gets his proof when Claudius reacts so violently to the players' reenactment of Old Hamlet's death (staged by Hamlet). Hamlet wants only to pursue his revenge if it is justified and honest.
Laertes, on the other hand, resorts to duplicity and cowardice. Rather than collecting hard evidence and attempting to understand what actually happened between his father and Hamlet, Laertes shows up at court with the news of his father's murder, demanding to see Claudius. Claudius is deceitful and manipulative, presenting Hamlet as the villain. When Laertes asks why Claudius did not take action against Hamlet, the King lies: he does not want to hurt Gertrude who adores her son; and, Hamlet is a favorite with the citizens of Denmark. Laertes allows himself to be used as Claudius' puppet. The King stirs Laertes' sorrow into hatred until Laertes can no longer see reason.
By this time, Ophelia has lost her mind. Laertes places the blame for this and her father's death with Hamlet. He vows revenge.
Claudius goes about twisting Laertes' mind. He asks him if he loved his father or if his reaction is all for show. He shares the need for urgency—that they must act immediately if the deed is to be done. Claudius instructs Laertes that if they only talk about what they should do, the desire for vengeance will fade away. So the King asks Laertes:
What would you undertake
To show yourself your father's son in deed? (IV.vii.135-136)
Claudius wants Laertes to prove what he is willing to do to make Hamlet pay for Polonius' murder and Ophelia's insanity. Laertes' response is blasphemous, showing that he has no compunction about the state of his soul—he is not worried about being punished in the next world. Laertes responds that he would be willing...
To cut his throat i' the church. (137)
Ultimately, Hamlet chooses not to kill Claudius when it seems the King is praying—when Hamlet believes he is asking forgiveness for his sins because the prince does not want the King's soul to face eternity without sin when Old Hamlet had no chance to confess his sins.
It is Hamlet's hesitation that provides Claudius with the opportunity to make arrangements with Laertes. He will pretend to make peace with Hamlet at a fencing contest. Hamlet is unaware that the blade of the fencing sword is sharpened and tainted with poison. This demonstrates Laertes' cowardice. Hamlet and Laertes are both cut with the envenomed blade. Realizing the King's treachery too late, Laertes does ask Hamlet's forgiveness and dies. Hamlet soon follows.
Hamlet and Laertes are foils—they are (from a literary/dramatic standpoint) very similar: both have lost a beloved father. Both vow revenge. They are foils because by comparison the audience is more clearly able to see how different the two men really are—(with an emphasis on our tragic hero) particularly in the way each man chooses to react to his father's death. Laertes allows his rage to overpower common sense and his longstanding relationship with Hamlet [at court], and willingly accepts Claudius' scurrilous plan to kill Hamlet in an unfair fight. On the other hand, Hamlet looks for proof that his actions will be justified.