Iago is using his assumption of women, and in this specific case of Desdemona, to manipulate Roderigo into thinking that WHEN Desdemona leaves Othello (Because according to him she will grow tired of him, his older age, and his bad looks) she will go after Cassio. Iago is telling Roderigo that Cassio is the obvious next choice. “The knave is handsome, young, and hath all those requisites in him that folly and green minds look after. A pestilent complete knave, and the woman hath found him already. (247-251) He starts feeding Roderigo’s mind with ideas that, Desdemona has already started flirting with Cassio, and flirtation eventually leads to sexual relations. “Lechery, by this hand, an index and obscure prologue to the history of lust and foul thoughts. They met so near with their lips that their breaths embraced together.” (260-263)

Iago sees that the love Othello and Desdemona share is deep, and because of this love Othello would do anything to please Desdemona. He assumes women have a certain power over men that allow them to do as they please. “That she may make, unmake, do what she list.”(334) He uses this knowledge to his advantage to convince Cassio to reach out to Desdemona and beg her to speak to her husband in his behalf. While this is happening Iago is going to be instilling suspicion in Othello’s mind about Cassio and Desdemona.

In all of Act II, Iago draws on assumptions to execute his master plan.