The difference between blank verse and prose lies in the rhythm, but it can certainly be more difficult to identify the difference between the two in the works of early modern writers other than Shakespeare—simply because, if we are used to the works of Shakespeare, where the distinction is very clear, the writing of a playwright like Webster will seem less rhythmic. Shakespeare's blank verse tends to use very regular iambic pentameter—each line spoken will have five clear points of emphasis, each of which is known as a foot, or iamb.
Webster's language here is less distinctive. However, he adheres to the same general set of rules for versification as other playwrights of the time: namely, iambic pentameter is used to indicate a character of higher rank, whereas more common characters will speak in prose. Occasionally, rhymed verse will be used, often to end a scene.
Webster marks out the first full line of the Duchess's speech in clear iambic pentameter to make it obvious that she is,...
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