If Edgar can reveal his thoughts and plans through soliloquy, it is only fair that his bastard brother, Edmund, would get the chance to do the same. In Act 1, Scene 2, Edmund finally gets the opportunity to air his grievances directly to the audience.
Thou, Nature, art my goddess. To thy law
My services are bound. Wherefore should I
Stand in the plague of custom, and permit
The curiosity of nations to deprive me
For that I am some twelve or fourteen moonshines
Lag of a brother? Why “bastard?” Wherefore “base,”
When my dimensions are as well compact,
My mind as generous and my shape as true
As honest madam’s issue? Why brand they us
With “base,” with “baseness,” “bastardy,” “base,"
[...]
Edmund the base
Shall top th' legitimate. I grow, I prosper.
Now, gods, stand up for bastards!
Edmund uses this soliloquy to express his intense anguish at being the bastard son while his legitimate brother, Edgar, enjoys all the rights of a legitimate heir. Setting up the tension and drama to come, he announces his allegiance to no human being but to nature herself, thereby establishing himself as an untrustworthy and fundamentally self-serving character. His goals, as stated, will be to claim the land he believes is rightfully his and to vanquish his brother. With this in mind, the audience sets forth through the rest of the play properly attuned to Edmund’s sinister ambitions, allowing Shakespeare to later create spectacular dramatic irony by playing Edmund's deceit and doublespeak against what the audience now knows about his true allegiances.
As characters change their clothes, their manners of speech, and even their entire identities, Shakespeare uses the soliloquy as a crucial device to clue the audience in on the inner machinations guiding even the most outwardly insane behavior. In Act 2, Scene 4, after Gloucester disinherits Edgar and casts him out from his hold, Edgar undertakes a startling transformation and reveals his thought process to the audience:
Whiles I may ’scape,
I will preserve myself, and am bethought
To take the basest and most poorest shape
That ever penury in contempt of man
Brought near to beast. My face I’ll grime with filth,
Blanket my loins, elf all my hair in knots,
And with presented nakedness outface
The winds and persecutions of the sky.
The country gives me proof and precedent
Of Bedlam beggars, who with roaring voices
Strike in their numbed and mortified bare arms Pins, wooden pricks, nails, sprigs of rosemary,
[…]
“Poor Turlygod!” “Poor Tom!"
That’s something yet. Edgar I nothing am.
This soliloquy offers a vital opportunity for the audience to witness Edgar’s adoption of the “Poor Tom” moniker and his descent into a practiced sort of mock-insanity that Edgar hopes will keep him safe despite his newfound status as an outlaw in the kingdom. It also tees up a slew of scenes rife with dramatic irony: where the audience knows Poor Tom to be Edgar, the various characters in King Lear are able to make no such distinction. By cluing the audience into Edgar’s plans, then, Shakespeare is able to build and sustain tension throughout the remainder of the play as Edgar attempts to maneuver himself back into his father’s graces.
