Finally the one way the poet was to achieve relief, to become an independent Self, was to kill her father’s memory, which, in "Daddy," she does by a metaphorical murder. Making him a Nazi and herself a Jew, she dramatizes the war in her soul. It is a terrible poem, full of blackness, and one of the most nakedly confessional poems ever written. From its opening image onward, that of the father as an "old shoe" in which the daughter has lived for thirty years—an explicitly phallic image, according to the writings of Freud—the sexual pull and tug is manifest, as is the degree of Plath’s mental suffering, supported by references to Dachau, Auschwitz, and Belsen. (Her references elsewhere to hanged men are also emblems of suffering; in Jungian psychology, the swinging motion would be symbolic of her ambivalent state and her unfulfilled longing as well.) Plath confesses that, after failing to escape her predicament through attempted suicide, she married a surrogate father, "a man in black with a Meinkampf look" who obligingly was just as much a vampire of her spirit—one who "drank my blood for a year, / Seven years, if you want to know." (Sylvia Plath was married to the poet Ted Hughes for seven years.) When she drives the stake through her father’s heart, she not only is exorcising the demon of her father’s memory, but metaphorically is killing her husband and all men.
"Daddy" is a poem of total rejection. When she writes that "the black telephone’s off at the root," she is turning her back on the modern world as well. Such rejection of family and society leads to that final rejection, that of the Self. Her suicide is everywhere predicted, in poems of symbolic annihilation such as "Totem" and in statements of human fascination with death. In "Edge," to be dead is to be perfected! Her earlier terror at death, thus, becomes a romance with it, and her poems themselves are what M. L. Rosenthal calls "yearnings toward that condition." Freud believed the aim of all life is death, and for Plath life was poetry. So by extension, poetry for her now becomes death, both conditions inseparable. She as much as says so: "The blood jet is poetry, / There is no stopping it."
From "The Dark Tunnel: A Reading of Sylvia Plath." Modern Poetry Studies 3.2 (1972).