Death
Death is an ever-present reality in Plath's poetry, and manifests in
several different ways.
Death is dealt with in terms of suicide, which eerily corresponds to her
own suicide attempts and eventual death by suicide. In "Lady
Lazarus," she claims that she has mastered the art of dying after trying
to kill herself multiple times. She sneers that everyone is used to crowding in
and watching her self-destruct.
Suicide, though, is presented as a desirable
alternative in many of these works. The poems suggest it would release her from
the difficulties of life, and bring her transcendence wherein her mind could
free itself from its corporeal cage. This desire is exhilaratingly expressed in
"Ariel," and bleakly and resignedly expressed in "Edge."
Death is an immensely vivid aspect of Plath's work, both in metaphorical and
literal representations.
Victimization
Plath felt like a victim to the men in her life, including her father, her
husband, and the great male-dominated literary world. Her poetry can often be
understood as response to these feelings of victimization, and many of the
poems with a male figure can be interpreted as referring to any or all of these
male forces in her life.
In regards to her father, she realized she could never escape his terrible
hold over her; she expressed her sense of victimhood in "The
Colossus" and "Daddy," using powerful metaphors and comparisons
to limn a man who figured heavily in her psyche.
Her husband also victimized her through the power he exerted as a man, both
by assuming he should have the literary career and through his infidelity.
Plath felt relegated to a subordinate, "feminine" position which
stripped from her any autonomy or power. Her poems from the
"Colossus" era express her frustration over the strictures under
which she operated. For instance, "A Life" evokes a menacing and
bleak future for Plath. However, in her later poems, she seems finally able to
transcend her status as victim by fully embracing her creative gifts
("Ariel"), metaphorically killing her father ("Daddy"), and
committing suicide ("Lady Lazarus", "Edge").
Patriarchy
Plath lived and worked in 1950s/1960s England and America, societies
characterized by very strict gender norms. Women were expected to remain safely
ensconced in the house, with motherhood as their ultimate joy and goal. Women
who ventured into the arts found it difficult to attain much attention for their
work, and were often subject to marginalization and disdain. Plath explored and
challenged this reductionist tendency through her work, offering poems of
intense vitality and stunning language. She depicted the bleakness of the
domestic scene, the disappointment of pregnancy, the despair over her husband's
infidelity, her tortured relationship with her father, and her attempts to find
her own creative voice amidst the crushing weight of patriarchy. She shied away
from using genteel language and avoided writing only of traditionally
"female" topics. Most impressively, the work remains poetic and
artistic - rather than political - because of her willing to admit ambivalence
over all these expectations, admitting that both perspectives can prove a trap.
Nature
Images and allusions to nature permeate Plath's poetry. She often evokes
the sea and the fields to great effect. The sea is usually associated with her
father; it is powerful, unpredictable, mesmerizing, and dangerous. In
"Full Fathom Five," her father is depicted as a sea god. An image of
the sea is also used in "Contusion," there suggesting a terrible
sense of loss and loneliness.
Nature is also manifested in the bright red tulips which jolt the listless
Plath from her post-operation stupor, insisting that she return to the world of
the living. Here, nature is a provoker, an instigator - it does not want her to
give up. Nature is a ubiquitous theme in Plath's work; it is a potent force
that is sometimes unpredictable, but usually works to encourage her creative
output.
The self
Plath has often been grouped into the confessional movement of poetry. One
of the reasons for this classification is that she wrote extensively of her own
life, her own thoughts, her own worries. Any great artist both creates his or
her art and is created by it, and Plath was always endeavoring to know herself
better through her writing. She tried to come to terms with her personal
demons, and tried to work through her problematic relationships. For instance,
she tried to understand her ambivalence about motherhood, and tried to vent her
rage at her failed marriage.
However, her exploration of herself can also be understood as an
exploration of the idea of the self, as it stands opposed to society as a whole
and to other people, whom she did not particularly like. Joyce Carol Oates
wrote that even Plath's children seemed to be merely the objects of her
perception, rather than subjective extensions of herself. The specifics of
Plath's work were drawn from her life, but endeavored to transcend those to ask
more universal questions. Most infamously, Plath imagined herself as a Jew,
another wounded and persecuted victim. She also tried to engage with the idea
of self in terms of the mind and body dialectic. "Edge" and
"Sheep in Fog" explore her desire to leave the earthly life, but
express some ambivalence about what is to come after. "Ariel"
suggests it is glory and oneness with nature, but the other two poems do not
seem to know what will happen to the mind/soul once the body is eradicated.
This conflict - between the self and the world outside - can be used to
understand almost all of Plath's poems.
Motherhood
Motherhood is a major theme in Plath's work. She was profoundly ambivalent
about this prescribed role for women, writing in "Metaphors" about
how she felt insignificant as a pregnant woman, a mere "means" to an
end. She lamented how grotesque she looked, and expressed her resignation over
a perceived lack of options. However, in "Child," she delights in her
child's perception of and engagement with the world. Of course,
"Child" ends with the suggestions that she knows her child will
someday see the harsh reality of life. Plath did not want her children to be contaminated
by her own despair. This fear may also have manifested itself in her last poem,
"Edge," in which some critics have discerned a desire to kill her
children and take them with her far from the terrors of life. Other poems in
her oeuvre express the same tension. Overall, Plath clearly loved her children,
but was not completely content in either pregnancy or motherhood.
Source: http://www.gradesaver.com/sylvia-plath-poems/study-guide/major-themes/
These images depict the theme of death by describing a corpse. Thus, the imagery of death establishes that in order to be born again, she need suffer and die before. 
