In these soliloquies, which occur early on in the play, Shakespeare gives the audience their first insight into the shadowy character of Edmund. He also begins to explore several significant themes of the play such as nature and the natural, social custom and fate.
Firstly, Edmund personifies "nature" as a "goddess" and declares his allegiance to her. His reasoning is that he should be taken just as seriously by society as Edgar, his "legitimate" brother, because he was conceived at the height of sexual passion outside of wedlock, whereas Edgar was conceived "within a dull, stale, tired" marriage bed. He argues that the lustful sex at his conception has given him more natural vitality, "More composition and fierce quality", so he scorns the lower status he has to endure as an illegitimate child. (We can see his scorn in Shakespeare's alliteration on "b" sounds and vigorous repetition to show Edmund's fierce disdain of the way society treats him: "Why brand they us / With base? with baseness? bastardy? base, base?") So, through this speech, Shakespeare is exploring the theme of natural power. Edmund's youth and vitality leads him towards power and he decides to override the normal social restrictions he would otherwise have to endure as a "bastard". Note the natural imagery he uses towards the end of the first soliloquy as he states, "I grow; I prosper." It is as though he is a healthy plant who will inevitably gain strength. We also see this theme as the play progresses, as the young, sexualised sisters, Regan and Goneril, claim increasing political power, whilst Lear seems to age before the audience's eyes. Shakespeare seems to be asking whether physical vigour, nature, is ultimately able to triumph over the existing social order.
Another theme which arises in these two soliloquies is social custom. Edmund is scathing about "the excellent foppery of the world" and "the plague of custom". He shows huge frustration about the usual processes by which decisions are made in his society. He seems to disassociate himself from the powerful people who make decisions, calling them, "they", showing he doesn't feel integrated into society. In the second soliloquy, he mocks his father for believing that "the sun, the moon, and the stars" have influence over events. The usual social custom of reading occurences in relation to astrology seems ridiculous to Edmund. Shakespeare is questioning the power of social customs to shape lives as Edmund feels limited and angered by the labels he has had to live with.
Another theme which Shakespeare handles here is fate. This is a core theme of the play. In Edmund's second soliloquy, he sarcastically lists the ways that people hand over responsibility for their actions to "the stars" and claim they are "fools by heavenly compulsion". In this way, Edmund is suggesting that we actually hold our own fate in our hands and he scorns the idea that it might already be decided. This is an issue which Shakespeare addresses in the whole play. Through the central sections of the play, the audience sees the political strengthening of the least moral characters, whereas the noblest characters are ostracised and reduced to beggarly figures. By the end of the play, many characters have died, though two of the noblest, Edgar and Albany, survive to take power. This leaves the audience questioning whether there really is any heavenly power or fate in control of what happens.