The subplot of Polonius' relationship with his children highlights the lack of genuine family relationships at the Danish court. As with everything else at Elsinore, power, not love, is what determines relations between Polonius and his children. We can never know for sure if Polonius does indeed love his children. If so, he has a funny way of showing it.

Once he's bid farewell to Laertes, who's off to Paris for his studies, Polonius immediately instructs one of his lackeys to go with his son to France, where he is to spy on him. Once there, he's to put it about that Laertes is involved in a debauched lifestyle. How people react to such news will determine whether or not Laertes really has been a naughty boy. Most normal parents would balk at such ruthless manipulation of their children's lives. But not Polonius. As a hardened veteran of the Danish court, such power moves are second nature to him.

Even worse is his manipulation of Ophelia, whom he shamefully uses as a pawn in an elaborate game to determine the reasons behind Hamlet's unusual behavior. Ophelia is emotionally destroyed by the experience, yet Polonius doesn't seem to care. As always, he's only interested in the political consequences of Hamlet's vicious rant against his daughter.

Once again, we see how proximity to power distorts family relationships, which, as with all royal courts, are determined by power rather than by bonds of love and affection.

The subplot involving Polonius, Ophelia, and Laertes is crucial to the central plot in several ways.

First, the relationship between Laertes and Polonius parallels that between Hamlet and his dead father; in this respect, Laertes serves as a foil for Hamlet. The theme that a son must avenge his father’s death joins the two stories. Their duel kills both young men.

Second, Polonius’s position at court and his hypocritical behavior emphasize the play’s overall theme of corruption: he exemplifies what is “rotten” in the Danish court. Incapable of following his own advice, “to thine own self be true,” Polonius is a total sycophant. His complicity in the monarch’s schemes, by hiding behind the arras, leads to his death.

Third, Polonius’s treatment of his daughter and his acquiescence of the monarchy using her to bait and spy on Hamlet, while generally related to the hypocrisy theme, is crucial to the main plot. Her father’s behavior endangers Ophelia by making Hamlet further suspect Claudius and Gertrude’s plot and also helps destroy her relationship with Hamlet. This directly or indirectly leads to her death. Depending on one’s interpretation, as Shakespeare leaves it ambiguous, either Gertrude kills Ophelia by pushing her the river, or Ophelia kills herself by jumping in.