Polonius asks Reynaldo to keep an eye on his son, Laertes staying in Paris. In fact, Polonius wants evidence and proof whether his son is indulged into drinking, fighting and doing other bad activities or not. Because has been just speculating and heard about it without finding any proof is in his hands yet. Therefore, he gives this role of spying to Reynaldo in order to bring the proof of his son’s bad behavior.
Why Polonius Asks Reynaldo to spy on his Son, Laertes?