What are Cordelia's and The Fool's dramatic functions in the play King Lear?
The gentle, loving Cordelia is a foil to her two greedy, unloving sisters, Goneril and Regan. If Shakespeare had given Lear only the two heartless daughters, it would have suggested that all daughters are like these two. But that was not the playwright's apparent intention. Shakespeare had to have good characters to show that his view of humanity was not entirely negative. Kent, Edgar, Gloucester, Cordelia, and the Fool are all good characters.
The Fool's main function in the play is to serve as a companion and confidant of King Lear after the old man becomes disillusioned with Goneril and Regan and is also beginning to feel shame and regret for the way he treated his one sincere daughter because she refused to flatter him. Also, King Lear is supposed to have a hundred knights as companions and escorts, but Shakespeare could not show all or any part of such a large body of men on the stage. The Fool serves to represent Lear's retinue and to illustrate the kind of annoyance Lear causes Goneril with his boisterous and unruly followers. The Fool, in effect, represents all one hundred knights. But most importantly, Lear has to have someone to talk to when there is no one else present. Otherwise, Lear would have to indulge in many soliloquies. The audience cannot be looking at a character who is all alone on the stage and understand what that character is thinking, feeling, remembering, planning, etc. There has to be dialogue, and the Fool is used as an interlocutor.