The Devolution of Satan in Paradise Lost

Oh, What a Pretty Snake!
The Devolution of Satan
in Paradise Lost

Aesop may have met Milton's Satan at some point in his career. Just before the beginning of Paradise Lost Satan has not become the serpent many now consider the symbol of evil incarnate; he is yet only a fox:
One hot summer's day a Fox was strolling through an orchard till he came
to a bunch of Grapes just ripening on a vine which had been trained over a
lofty branch. "Just the thing to quench my thirst," quoth he. Drawing back
a few paces, he took a run and a jump, and just missed the bunch. Turning
round again with a One, Two, Three, he jumped up, but with no greater
success. Again and again he tried after the tempting morsel, but at last had
to give it up, and walked away with his nose in the air, saying: "I am sure
they are sour." Aesop, Best-Loved Folktales of the World

Let us examine how and why Satan, once the brightest star in the heavens, eventually finds himself transformed into a lowly, crawling thing. His journey begins with a vague longing, but he will not remain a dissatisfied vulpine figure with much good still in him for very long. Readers will watch him pass through willful assumption of ophidian form to a state wherein his transformation is no longer of his choosing, although he has inarguably brought it upon himself.
Picture it: Satan, most beautiful of the angels by many accounts, wanders Heaven and wonders, perhaps, why he hasn't power to match his real or imagined beauty. Though created able to withstand the encroachment of such base impulses, he is not fitted out with impregnable armor against them. As C.S. Lewis points out in Chapter 10 of A Preface to Paradise Lost, Milton insists on the "excellence of Satan's Nature . . . in contrast to, and aggravation of, the perversion of his will". Like Adam and Eve, he could be considered innocent, having not yet transgressed. Also like them, he is not virtuous. The perceived injustice of it grows within him, just as it does later in Eve when he infects her with it.
When Book One begins, Satan has missed his bunch of grapes for the last time and been hurled into the lake of fire for his troubles. His discontent reached critical mass offstage, and since God did not give him what he wanted (whether he asked politely or went straight into Cosmic Tantrum Mode is unclear) he has tried to take it by force.
Chained and burning, he hurtles headlong into his first logical fallacy. Satan's entire argument, from beginning to end, is based on a "sence of injur'd merit". He seems to believe that God did an outstanding job creating him, and that he is such a masterpiece that he deserves much, much more than he's got. The idea that he sprouted from the soil like an odd sort of radish has not yet occurred to him. And yet, he seems surprised that a being with the power to casually produce such a work of wonder as himself can also, at will, squash him like a bug. Consider Satan's own words on the matter:
From what highth fall'n, so much the stronger prov'd He with his
Thunder: and till then who knew The force of those dire Arms? yet
not for those, Nor what the Potent Victor in his rage Can else inflict
do I repent or change . . . Milton, Paradise Lost 1: 92
He is admitting that God was able to pitch him and the third of Heaven's host that made up his incredibly ill-advised army out of Heaven and into an unholy cauldron of fire, and furthermore, that God could probably do the rebels a far worse turn if He so desired.
In addition, what he must know but does not admit aloud and only possibly to himself is that God not only is capable of such, but did it by delegation! Unless Satan is far less intelligent than the available evidence indicates, he must know that the rebels never got close to the Throne. God told Michael to go take care of it. Therefore, his pride can't allow him to voice the fact that it wasn't God but a mere minion of God who so easily disposed of the rebel army.
What this means is he is able, somehow, to maintain a belief in his own superiority over all the other angels, and maybe his equality to God Himself in spite of the fact that he has been absolutely trounced not by God, but by another angel holding orders signed "God Almighty, by direction".
It seems impossible that he could believe this, so perhaps he is lying to save face. In this instance, it is not clear what he really believes, although later he does many things to earn his title "The Father of Lies". The rigged debate of Book Two is as slick a piece of deception as history or literature has ever seen, despite consisting of lies of manipulation rather than vocalized falsehoods. That he lies to Eve is indisputable. In order to fool the sharp-sighted Uriel, he must have put on a wonderful performance as a harmless, worshipful cherub. Sin may not catch on, but Satan claims to have come to free Sin and Death after claiming he knew nothing of their existence. He tells his own troops that their "exile Hath emptied Heav'n"; the amusing bit is that none of them wonder just who it was God used for troops if Satan recruited all of Heaven's host. Satan is the consummate liar, so much so that he will eventually in a sense be consumed by the lies and lose the ability to distinguish truth from untruth.
Self-delusion isn't Satan's only problem. A psychiatrist might diagnose him manic-depressive. It is obvious that he is at times quite full of the idea of his own grandeur, but at other times, he is in the deepest despair. We see by Satan's acts that he thinks well of himself, but Milton actually tells us about the despair in line 126 of Book One. Let's believe him; it is his epic, after all.
Satan also has to be ambivalent about his dual character. Hearken back to what C.S. Lewis wrote about the excellence of Satan's nature as opposed to his will. Religious doctrine held that evil was not a palpable force, but was instead the absence of good. Milton believed this, therefore Satan as written by Milton must be at least partly good. Otherwise, he would collapse completely, being entirely void of substance. Satan shows that his erosion is incomplete in Book Four, when he sits hidden to observe Adam and Eve. He is moved by them, which can only mean that there is something yet in him to be touched:
O Hell! what doe mine eyes with grief behold, Into our room of bliss
thus high advanc't 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 formd them on thir shape hath
poured. Milton, Paradise Lost 4 : 358
The idea that the best villains are perverted servants of good has something to it, because it has lasted a very long time. Consider an example from modern popular culture: Darth Vader. In his films Star Wars, The Empire Strikes Back, and Return of the Jedi, George Lucas makes use of the same theory. The nastiest, toughest figure opposing the heroes was once a very good man. The Emperor, who is more evil than Vader, is destroyed by Vader despite the fact that he is also supposed to be more powerful. This illustrates the point that Darth Vader's power comes from that core of good. It is exactly the same with Satan, even though all of his evil comes to good in the end. He is a very powerful, unwilling servant of God who zooms hither and thither on missions of utter perversion, with God on the other end of the leash all the while.
God has apparently planned it this way, having foreknowledge that despite being issued a perfectly good nature, some creatures will choose to be evil. God will then use the evil creatures to produce more good. Satan may or may not be consciously aware of this puppet show he's starring in, but it is sure that every time he catches sight of redemption he flees. In Book Three, Satan stands before the Gates of Heaven in all their splendor, where he views the magnificence of our world below. It is a sight that makes him catch his breath: Milton tells us that he "looks down with wonder". Again, that little bit of good in him resonates with what he sees. He looks on what God has wrought and it moves him. So :
. . .without longer pause Down right into the Worlds first region throws
His flight precipitant . . . Milton, paradise Lost 3 : 561
The tiniest inkling of his own goodness, and, as it follows, that God had something to do with his being scares the Hell out of Satan. This is the most extreme example, because he is literally standing on God's pearly front porch, but it happens more than once that he flees from the awful specter of redemption and forgiveness.
Beyond manic-depressive tendencies, delusions of grandeur, selfishness, and a growing inability to distinguish lies form truth, what else is there to Satan? Well, he's also got another childish trait. Having taken a sound whipping from God the Father, he immediately hits on a scheme to make himself feel better: he will go beat up on someone smaller. (Add reference to Stranger in a Strange Land? The scene where Mike gets humor?) It is well accepted that people insult and hurt other people to boost their own self-images. Satan's feelings of power and might have taken a bruising, so he needs a little bit of easy victory to set himself right. He has to find someone weaker to abuse, or his illusions of supremacy on which he has based his whole worldview might vanish. If those illusions did disappear, he would be in trouble deeper than the blackest pit of Hell. He would have to admit that he was wrong. Then he would have to explain to his followers that he was wrong. They would probably not be amused. Even if they did not destroy him, they certainly would not look up to him anymore. He would then have to see himself as the lowest of the low, when he had considered himself the highest of the high. It is so much easier to just go and find someone to kick around until he feels better. Besides, that way he also gets back at God, or so he believes.
In Book Ten the corruption of Adam and Eve has been completed. Satan has returned triumphant to his waiting army. However, Satan's project of corruption is not the only thing being completed. Up until his return, Satan's nefarious acts have been volitional. He has willingly been the serpent. Not any longer: the applause he expects does not come. Instead:
. . . he hears On all sides, from innumerable tongues A dismal universal
hiss, the sound of public scorn; he wonderd, but not long Had leisure,
wondring at himself now more; His Visage drawn he felt to sharp and
spare, His Armes clung to his Ribs, his Leggs entwining Each other, till
supplanted down he fell A monstrous Serpent on his Belly prone,
Reluctant, but in vain, a greater power Now rul'd him . . .
Milton, Paradise Lost 10 : 506
Now Satan has finished his transformation from brightest of angels to basest of beasts. He isn't in charge any more, if ever he was. Furthermore, all his minions are transformed with him. Their dismal hissing brings the curtain down on Satan's part in Paradise Lost.