After Cordelia is hanged, Lear initially seems to accept his loss. "I know when one is dead," he proclaims. "She's dead as earth" (5.3.3). Yet, a few moments later, Lear sees a feather stir upon Cordelia's lips, which leads him to believe that his beloved daughter is breathing and still somehow alive. "This feather stirs," he says, "she lives!"(5.3.4). What's going on here? Why does Lear think Cordelia is still breathing when it's obvious that she is not? How can a man stand over his daughter's dead body and convince himself that she's alive?
It seems that Lear experiences something pretty common and universal at this moment in the play. When we suffer a traumatic loss, we often hold out hope that a loved one is somehow still alive (this often happens despite concrete evidence to the contrary). Because it's often just too painful to accept, we often tell ourselves "Maybe it's not really true – this must be a terrible mistake." It seems that Cordelia's tragic death is just too painful for her father to accept and he convinces himself that it isn't really true. The feather, then, functions as a symbol of Lear's denial, one of the most common elements of grief.