Why did shakespheres noble characters speak in iambic pentameter while commoners spoke mainly in blank verse or prose

1. First, Shakespeare wrote his plays in blank verse featuring iambic pentameter because that was the style of the day. Think of it as a way for an author to show off--and it really is quite impressive if one thinks about it. There are very few authors who can create characters and plots as rich as Shakespeare's and write their lines in a consistent meter. 2. Secondly (I think that this might be what you are asking), when Shakespeare's characters speak in verse (iambic pentameter), they are usually the noble (aristocratic) characters, and their speech represents their high culture and position in society. If you simply look at one of Shakespeare's plays, you can often tell when the commoners are speaking because their lines will go from margin to margin (this is true, too, of nobles who are acting like commoners--whether they're involved in evil schemes, losing their minds, or are drunk!). In contrast, Shakespeare's other characters' lines should sound and look different to you--they should sound "sing-songy" and should look like poetry with uneven lengths. A good example of this is from Othello. When Iago is speaking to his peers or to those in position of authority over them, his speech is in verse, but when he is plotting and talking to Roderigo (especially at the play's beginning), his lines are not in iambic pentameter--this represents the bawdy nature of his speech and, in truth, the baseness of his character.