Synthesized answer
Polonius believes that a "bait of falshood" catches a "Cape of truth" by using "windlesses" and "assaies of Bias" [1]. Through these indirect methods, Polonius explains, one can discover the truth about someone [1]. He elaborates on this by instructing Reynaldo to spread subtle falsehoods or "slight sulleyes" about his son, Laertes [3]. By voicing these fabricated faults, Polonius believes the person they are speaking to will feel compelled to agree and confirm the supposed misdeeds, thereby revealing what they know about the individual [3].
For example, Polonius suggests that if Reynaldo mentions Laertes engaging in activities like gaming, drinking, fencing, swearing, quarreling, or visiting brothels, the person Reynaldo is questioning will likely respond by confirming these or similar actions, thus providing the "Cape of truth" [2, 1]. Polonius states that by laying these minor accusations, the person being sounded out will "closes with you in this consequence" [3].
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
There falling out at Tennis; or perchance, I saw him enter such a house of saile; Videlicet, a Brothell, or so forth. See you now; Your bait of falshood, takes this Cape of truth; And thus doe we of wisedome and of reach With windlesses, and with assaies of Bias, By indirections finde directions out: So by my former Lecture and aduice Shall you my Sonne; you haue me, haue you not? Reynol. My Lord I haue Polon. God buy you; fare you well Reynol. Good my Lord Polon. Obserue his inclination in your selfe Reynol. I shall my Lord Polon. And let him plye his…
now his father and his friends, And in part him. Doe you marke this Reynoldo? Reynol. I, very well my Lord Polon. And in part him, but you may say not well; But if't be hee I meane, hees very wilde; Addicted so and so; and there put on him What forgeries you please; marry, none so ranke, As may dishonour him; take heed of that: But Sir, such wanton, wild, and vsuall slips, As are Companions noted and most knowne To youth and liberty Reynol. As gaming my Lord Polon. I, or drinking, fencing, swearing, Quarelling, drabbing. You may goe so farre Reynol. My Lord…
Reynol. But my good Lord Polon. Wherefore should you doe this? Reynol. I my Lord, I would know that Polon. Marry Sir, heere's my drift, And I belieue it is a fetch of warrant: You laying these slight sulleyes on my Sonne, As 'twere a thing a little soil'd i'th' working: Marke you your party in conuerse; him you would sound, Hauing euer seene. In the prenominate crimes, The youth you breath of guilty, be assur'd He closes with you in this consequence: Good sir, or so, or friend, or Gentleman. According to the Phrase and the Addition, Of man and Country Reynol. Very…
hath importun'd me with loue, In honourable fashion Polon. I, fashion you may call it, go too, go too Ophe. And hath giuen countenance to his speech, My Lord, with all the vowes of Heauen Polon. I, Springes to catch Woodcocks. I doe know When the Bloud burnes, how Prodigall the Soule Giues the tongue vowes: these blazes, Daughter, Giuing more light then heate; extinct in both, Euen in their promise, as it is a making; You must not take for fire. For this time Daughter, Be somewhat scanter of your Maiden presence; Set your entreatments at a higher rate, Then a…
aer. Polon. What ist Ophelia he hath said to you? Ophe. So please you, somthing touching the L[ord]. Hamlet Polon. Marry, well bethought: Tis told me he hath very oft of late Giuen priuate time to you; and you your selfe Haue of your audience beene most free and bounteous. If it be so, as so tis put on me; And that in way of caution: I must tell you, You doe not vnderstand your selfe so cleerely, As it behoues my Daughter, and your Honour. What is betweene you, giue me vp the truth? Ophe. He hath my Lord of late, made many tenders Of his affection to me Polon. Affection,…