In Book 4, as Satan journeys to Paradise, he experiences "many doubts with himself" (as Milton notes in his preface to the Book), which he voices in a soliloquy that features a paradox:
Nay curs'd be thou; since against his thy will
Chose freely what it now so justly rues.
Me miserable! which way shall I fly
Infinite wrath, and infinite despair?
Which way I fly is Hell; my self am Hell;
And in the lowest deep a lower deep
Still threatening to devour me opens wide,
To which the Hell I suffer seems a Heav'n.
O then at last relent: is there no place
Left for repentance, none for pardon left?
Previously, Satan has seemed ebullient and confident—proud of his decision to defy God and rebel against Heaven—but as he reaches Paradise, he begins to experience regret: not merely because he has been cast out of Heaven and lost God's favor, but because he feels he is "Hell" himself: irredeemably evil. This soliloquy shatters the reader's prior expectations for Satan, humanizing him as a character: as a tragic, multi-dimensional hero, he is not purely evil, but experiences chagrin and self-doubt, too.
Paradoxically, Satan likens the "Hell" he is suffering to "a Heav'n"—harkening back to what he has told Beelzebub earlier (in Book 1: "the mind is its own place, and in itself can make a heav'n of hell, a hell of heav'n"), as if to remind himself that he must accept his confinement in Hell, and attempt to seize power during his exile, treating Hell as if it were a Heaven.
This soliloquy—like another Satan soliloquy later in Book 4, after he spots Adam and Eve and experiences "love" for them—becomes a vehicle for Satan to work out and articulate his complicated emotions, while instructing himself to shore up courage and carry out his plot in Eden.
In Book 4, when Satan spots Adam and Eve in Eden for the first time, he is stunned by them, and reflects on their appearances in a soliloquy:
When Satan still in gaze, as first he stood,
Scarce thus at length failed speech recovered sad.
O Hell! What do mine eyes with grief behold,
Into our room of bliss thus high advanced
Creatures of other mould, earth-born perhaps,
Not Spirits, yet to Heav’nly Spirits bright
Little inferior; whom my thoughts pursue
With wonder, and could love, so lively shines
In them divine resemblance, and such grace
The hand that formed them on their shape hath poured.
Satan is alarmed to discover how serene and "advanced" Adam and Eve appear, and realizes that he "could love" them—they have a "divine resemblance" that seems to remind him of his own lost days in Heaven, and of the brilliance of God the Creator, who made them.
That Satan so quickly forgets his own plan to corrupt Adam and Eve—and is overwhelmed instead by their magnificence—shows that he is not totally corrupt or resigned to evil, but still wistful for Heaven, and the connection to divinity he has now lost: this realization (that Adam and Eve have what he no longer has) produces envy, which ultimately leads him to double-down on his plan to corrupt Eve.
This soliloquy also emphasizes Adam and Eve's pre-Fall splendor: even Satan is deeply impressed with them and views them as faultless beings (though he does not view God as faultless).
In Book 9, shortly before tempting Eve to eat from the Tree of Knowledge, Satan has a moment of doubt about his plan—but quickly resolves to follow through with it, expressing his decision in a soliloquy:
Thoughts, whither have ye led me, with what sweet
Compulsion thus transported to forget
What hither brought us, hate, not love, nor hope
Of Paradise for Hell, hope here to taste
Of pleasure, but all pleasure to destroy,
Save what is in destroying, other joy
To me is lost.
This soliloquy is a crucial moment for Satan's characterization. His first reaction, upon spotting Adam and Eve in Paradise, is to feel "love" and tenderness for them, even reveling in their beauty and innocence—though the reader may have previously assumed that he would be incapable of feeling love for anyone, especially the two humans whom God has vaunted as his most impressive creation (leading Satan to feel envious).
Instead, Satan must force himself to feel "hate" and remind himself that he can experience the "pleasure" that comes with love through a contradictory act: "destroying" Adam and Eve's "pleasure."
This soliloquy, then, helps the reader to understand Satan's tortured, divided mindset—establishing him as a complex character and effectively humanizing him.
In Book 9, Eve "muses" to herself in a soliloquy before deciding to eat the fruit from the Tree of Knowledge, using logos to support her decision:
Great are thy virtues, doubtless, best of fruits,
Though kept from man, and worthy to be admired,
Whose taste, too long forborne, at first assay
Gave elocution to the mute, and taught
The tongue not made for speech to speak thy praise:
Thy praise he also who forbids thy use,
Conceals not from us, naming thee the Tree
Of Knowledge, knowledge both of good and evil;
Forbids us then to taste, but his forbidding
Commends thee more, while it infers the good
By thee communicated, and our want:
For good unknown, sure is not had, or had
And yet unknown, is as not had at all.
Encouraged by Satan, Eve reasons that the fruit must be good, "though kept from man," because it miraculously conferred speech upon a formerly "mute" serpent. This inference is borrowed from Satan's own argument to Eve, in which he pretends that the fruit has given him the ability to speak. For Eve, this serves as evidence to justify her decision to seize the fruit: the serpent has not been punished for his decision, and therefore, Eve assumes she won't be, either. Moreover, Eve reasons that God's "forbidding," paradoxically, "commends" the fruit more. The fruit is so "good" that were she and Adam to know and enjoy its goodness, they would "want" it too badly; thus, God has prohibited them from eating the fruit in order to preserve it.
Eve also notes the Tree of Knowledge's ambiguous name, concluding that the fruit may not necessarily be harmful. The name suggests "knowledge both of good and evil," she says, which means that the fruit itself could confer divine knowledge of "good."
Unlike Satan, whose use of logos amounts to sophistry—a disingenuous argument intended to trick Eve—Eve is genuinely attempting to puzzle out why God might have placed this prohibition on her and Adam. Eve wants to reconcile what she already understands about the Tree—that "God hath pronounced it death to taste that Tree," as Adam reminds her—with what Satan has just told her: that the Tree's fruits have miraculous effects.
Though the reader is not always meant to sympathize with Eve, given the disastrous consequences of her transgression, this long soliloquy makes clear that Eve is thoughtful, curious, and reasonable—not simply rash and foolhardy. Her decision to eat the fruit has been thought-out and carefully considered, even if it is based on misleading temptation.
In Book 10, Adam is grief-stricken by the consequences of his and Eve's actions, which he reflects on in a long soliloquy:
O miserable of happy! is this the end
Of this new glorious world, and me so late
The glory of that glory? who now, become
Accursed of blessèd, hide me from the face
Of God, whom to behold was then my heighth
Of happiness: yet well, if here would end
The misery; I deserved it, and would bear
My own deservings; but this will not serve;
All that I eat or drink, or shall beget,
Is propagated curse. O voice once heard
Delightfully, Increase and multiply,
Now death to hear! for what can I increase
Or multiply, but curses on my head?
This is the longest soliloquy in the poem—previously, Adam has spoken to Eve in shorter monologues, and has not really expressed any complicated emotions or thought processes. Here, though, he grapples with his own guilt—realizing that he has not only disobeyed God's prohibition about the Tree of Knowledge, but also made it impossibly to "increase and multiply," as God has commanded him to do: he cannot joyfully reproduce with Eve, whom he views as a traitor. His allusion to "increase and multiply" may also refer to the impact of original sin on his offspring—that is, that any children he and Eve conceive will bear the same "curse" they've brought upon themselves.
The soliloquy ends with Adam asking for death: he feels that his life is irredeemable. Yet by admitting his own guilt, and confessing his feelings of despair and regret, he is supplicating God and the Son of God—which ultimately allows the Son of God to be merciful to him and Eve, and decide to sacrifice himself to redeem humankind. Therefore, this soliloquy has crucial narrative purpose—as opposed to being a straightforward lament.
