She uses the soliloquy in act 1 scene 2 (1.2.129-159) as a symbolic manifest, dividing the father figure into a positive sun god, Old Hamlet and a negative, incestuous satyr, Claudius. Then, likening Gertrude to an unweeded garden, the queen or rather her sexuality becomes the grounds for comparison for Hamlet, Adelman claims. The soliloquy is the textual evidence for Adelman's theory that the conflict in the play is more about the mother's remarriage as a vehicle of her sexuality than the loss of a father. The idealised father and Hamlet then become products of Gertrude's sexuality and the play proceeds with Hamlet's efforts to desexualise his mother, thus freeing himself and his father from her corruption. It is also worth noticing how her sexuality becomes synonymous with death; it lead to the death of Old Hamlet, Hamlet himself is its product with the terminal implication of origin and Old Hamlet's death also kills Hamlet's identity and leaves him in the power of his mother. Death becomes the sexualised Gertrude's legacy to her son.
However, the idealised father also played a role in relation to this sexuality. Adelman's response to this is to point out how Hamlet deflects the guilt of the father figure on Claudius while attributing most of the positive aspects to Old Hamlet. Later in her article, she also points out how Old Hamlet supposedly was able to control her sexuality (referring to the same soliloquy), making life livable for Hamlet. Therefore, the presence of the sexualised mother threatens the ideal of the idealised father being in control. Furthermore, it threatens to eliminate the oppositions between past and present, Old Hamlet and Claudius (both being subject to her sexuality) and the virginal image of Old Hamlet's wife and the "unweeded garden" of Claudius' wife. Finally, Hamlet's obsessing over Gertrude's appetite liken him to Claudius, the negative father image.
The central theme of the play, then, becomes the contamination of the female sexuality. Hamlet sees his mother's sexuality as a force which threatens his concepts of the world and causes its corruption. Adelman refers to what she calls "the deep fantasy of the play" (p.268) in which man is corrupted through contact with the corrupting female (seeing the act of intercourse as an origin of corruption) and in which the blame for the murder of the idealised father pass from Claudius to Gertrude. Her display of love becomes synonymous with murder, so much so that Claudius' political ambitions are subjugated to it and Hamlet in the closet scene (3.4) labels Gertrude the active murderer:
QUEEN GERTRUDE: O, what a rash and bloody deed is this!Hamlet initially fears the male under the power of a female and therefore withdraws into his antic disposition, an introvert mode of existence where he, the male and (ideally) the image of the idealised father, is in control and able to effectively impact the world around him without being affected.
HAMLET: A bloody deed! almost as bad, good mother, As kill a king, and marry with his brother.
QUEEN GERTRUDE: As kill a king!
HAMLET: Ay, lady, 'twas my word.
Sources: http://www.savagechickens.com/images/chickenpolonius.jpg and http://www.wsu.edu/~delahoyd/shakespeare/hamlete.jpg, last visited 14.2.2010
Janet Adelman in Shakespeare, William: Hamlet, ed. by Wofford, Susanne L., New York 1994