What contribution does Cassio make to the concerns and effects of the play 'Othello'?

Shakespeare presents Cassio as a balanced character, essentially honest and trustworthy, who, although he does have some weaknesses, he has weaknesses which are understandable and not in the extreme, thus contributing to the concerns and effects of weaknesses in Othello. He also provides a contrast to Iago, who seems to delight in evil, shown through the contrast of language between Iago and Cassio, which reflects their differences in social status. It is, in my opinion, …

…weaknesses of jealousy and his weakness to assume that others feel like he does about Desdemona. Cassio's treatment of Bianca would seem harsh in today's society, but the Jacobean audience would accept his using her as appropriate to her class and character and would recognize her acceptance of the arrangement. Cassio also has an unattractive awareness of the advantages of rank when he points out that "the lieutenant is to be saved before the ancient."