The Strong's Concordance number for the Hebrew word "Satan" is 07853 and 07854.

"7853 satan saw-tan' a primitive root; to attack, (figuratively) accuse:--(be an) adversary, resist."

"7854 satan saw-tawn' from 7853; an opponent; especially (with the article prefixed) Satan, the arch-enemy of good:--adversary, Satan, withstand."

The name commonly given to the fallen angels, who are also known as demons.  With the article (ho) it denotes Lucifer, their chief, as in Matthew 25:41, "the Devil and his angels".

It may be said of this name, as St. Gregory says of the word angel, "nomen est officii, non naturæ"--the designation of an office, not of a nature. For the Greek word (from diaballein, "to traduce") means a slanderer, or accuser, and in this sense it is applied to him of whom it is written "the accuser [ho kategoros] of our brethren is cast forth, who accused them before our God day and night" (Apocalypse 12:10). It thus answers to the Hebrew name Satan which signifies an adversary, or an accuser.

Mention is made of the Devil in many passages of the Old and New Testaments, but there is no full account given in any one place, and the Scripture teaching on this topic can only be ascertained by combining a number of scattered notices from Genesis to Apocalypse, and reading them in the light of patristic and theological tradition. The authoritative teaching of the Church on this topic is set forth in the decrees of the Fourth Lateran Council (cap. i, "Firmiter credimus"), wherein, after saying that God in the beginning had created together two creatures, the spiritual and the corporeal, that is to say the angelic and the earthly, and lastly man, who was made of both spirit and body, the council continues:

"Diabolus enim et alii dæmones a Deo quidem naturâ creati sunt boni, sed ipsi per se facti sunt mali." ("the Devil and the other demons were created by God good in their nature but they by themselves have made themselves evil.")

Here it is clearly taught that the Devil and the other demons are spiritual or angelic creatures created by God in a state of innocence, and that they became evil by their own act. It is added that man sinned by the suggestion of the Devil, and that in the next world the wicked shall suffer perpetual punishment with the Devil. The doctrine which may thus be set forth in a few words has furnished a fruitful theme for theological speculation for the Fathers and Schoolmen, as well as later theologians, some of whom, Suarez for example, have treated it very fully. On the other hand it has also been the subject of many heretical or erroneous opinions, some of which owe their origin to pre-Christian systems of demonology. In later years Rationalist writers have rejected the doctrine altogether, and seek to show that it has been borrowed by Judaism and Christianity from external systems of religion wherein it was a natural development of primitive Animism.

To this may be added the words of St. Jude: "And the angels who kept not their principality, but forsook their own habitation, he hath reserved under darkness in everlasting chains, unto the judgment of the great day" (Jude 1:6; cf. 2 Peter 2:4).

In the Old Testament we have a brief reference to the Fall in Job 4:18: "In his angels he found wickedness". But to this must be added the two classic texts in the prophets:

This parable of the prophet is expressly directed against the King of Babylon, but both the early Fathers and later Catholic commentators agree in understanding it as applying with deeper significance to the fall of the rebel angel. And the older commentators generally consider that this interpretation is confirmed by the words of Our Lord to his disciples: "I saw Satan like lightning falling from heaven" (Luke 10:18). For these words were regarded as a rebuke to the disciples, who were thus warned of the danger of pride by being reminded of the fall of Lucifer. But modern commentators take this text in a different sense, and refer it not to the original fall of Satan, but his overthrow by the faith of the disciples, who cast out devils in the name of their Master. And this new interpretation, as Schanz observes, is more in keeping with the context.

The parallel prophetic passage is Ezekiel's lamentation upon the king of Tyre:

There is much in the context that can only be understood literally of an earthly king concerning whom the words are professedly spoken, but it is clear that in any case the king is likened to an angel in Paradise who is ruined by his own iniquity.

Even for those who in no way doubt or dispute it, the doctrine set forth in these texts and patristic interpretations may well suggest a multitude of questions, and theologians have not been loath to ask and answer them. And in the first place what was the nature of the sin of the rebel angels? In any case this was a point presenting considerable difficulty, especially for theologians, who had formed a high estimate of the powers and possibilities of angelic knowledge, a subject which had a peculiar attraction for many of the great masters of scholastic speculation. For if sin be, as it surely is, the height of folly, the choice of darkness for light, of evil for good, it would seem that it can only be accounted for by some ignorance, or inadvertence, or weakness, or the influence of some overmastering passion. But most of these explanations seem to be precluded by the powers and perfections of the angelic nature. The weakness of the flesh, which accounts for such a mass of human wickedness, was altogether absent from the angels. There could be no place for carnal sin without the corpus delicti. And even some sins that are purely spiritual or intellectual seem to present an almost insuperable difficulty in the case of the angels. This may certainly be said of the sin which by many of the best authorities is regarded as being actually the great offense of Lucifer, to wit, the desire of independence of God and equality with God. It is true that this seems to be asserted in the passage of Isaiah (14:13). And it is naturally suggested by the idea of rebellion against an earthly sovereign, wherein the chief of the rebels very commonly covets the kingly throne. At the same time the high rank which Lucifer is generally supposed to have held in the hierarchy of angels might seem to make this offense more likely in his case, for, as history shows, it is the subject who stands nearest the throne who is most open to temptations of ambition. But this analogy is not a little misleading. For the exaltation of the subject may bring his power so near that of his sovereign that he may well be able to assert his independence or to usurp the throne; and even where this is not actually the case he may at any rate contemplate the possibility of a successful rebellion. Moreover, the powers and dignities of an earthly prince may be compatible with much ignorance and folly. But it is obviously otherwise in the case of the angels. For, whatever gifts and powers may be conferred on the highest of the heavenly princes, he will still be removed by an infinite distance from the plenitude of God's power and majesty, so that a successful rebellion against that power or any equality with that majesty would be an absolute impossibility. And what is more, the highest of the angels, by reason of their greater intellectual illumination, must have the clearest knowledge of this utter impossibility of attaining to equality with God. This difficulty is clearly put by the Disciple in St. Anselm's dialogue "De Casu Diaboli" (cap. iv); for the saint felt that the angelic intellect, at any rate, must see the force of the "ontological argument" (see ONTOLOGY). "If", he asks, "God cannot be thought of except as sole, and as of such an essence that nothing can be thought of like to Him [then] how could the Devil have wished for what could not be thought of?--He surely was not so dull of understanding as to be ignorant of the inconceivability of any other entity like to God" (Si Deus cogitari non potest, nisi ita solus, ut nihil illi simile cogitari possit, quomodo diabolus potuit velle quod non potuit cogitari? Non enim ita obtusæ mentis erat, ut nihil aliud simile Deo cogitari posse nesciret). The Devil, that is to say, was not so obtuse as not to know that it was impossible to conceive of anything like (i.e. equal) to God. And what he could not think he could not will. St. Anselm's answer is that there need be no question of absolute equality; yet to will anything against the Divine will is to seek to have that independence which belongs to God alone, and in this respect to be equal to God. In the same sense St. Thomas (I:63:3) answers the question, whether the Devil desired to be "as God". If by this we mean equality with God, then the Devil could not desire it, since he knew this to be impossible, and he was not blinded by passion or evil habit so as to choose that which is impossible, as may happen with men. And even if it were possible for a creature to become God, an angel could not desire this, since, by becoming equal with God he would cease to be an angel, and no creature can desire its own destruction or an essential change in its being. These arguments are combated by Scotus (In II lib. Sent., dist. vi, Q. i.), who distinguishes between efficacious volition and the volition of complaisance, and maintains that by the latter act an angel could desire that which is impossible. In the same way he urges that, though a creature cannot directly will its own destruction, it can do this consequenter, i.e. it can will something from which this would follow.

Although St. Thomas regards the desire of equality with God as something impossible, he teaches nevertheless (loc. cit.) that Satan sinned by desiring to be "as God", according to the passage in the prophet (Isaiah 14), and he understands this to mean likeness, not equality. But here again there is need of a distinction. For men and angels have a certain likeness to God in their natural perfections, which are but a reflection of his surpassing beauty, and yet a further likeness is given them by supernatural grace and glory. Was it either of these likenesses that the devil desired? And if it be so, how could it be a sin? For was not this the end for which men and angels were created? Certainly, as Thomas teaches, not every desire of likeness with God would be sinful, since all may rightly desire that manner of likeness which is appointed them by the will of their Creator. There is sin only where the desire is inordinate, as in seeking something contrary to the Divine will, or in seeking the appointed likeness in a wrong way. The sin of Satan in this matter may have consisted in desiring to attain supernatural beatitude by his natural powers or, what may seem yet stranger, in seeking his beatitude in the natural perfections and reflecting the supernatural. In either case, as St. Thomas considers, this first sin of Satan was the sin of pride. Scotus, however (loc. cit., Q. ii), teaches that this sin was not pride properly so called, but should rather be described as a species of spiritual lust.

Although nothing definite can be known as to the precise nature of the probation of the angels and the manner in which many of them fell, many theologians have conjectured, with some show of probability, that the mystery of the Divine Incarnation was revealed to them, that they saw that a nature lower than their own was to be hypostatically united to the Person of God the Son, and that all the hierarchy of heaven must bow in adoration before the majesty of the Incarnate Word; and this, it is supposed, was the occasion of the pride of Lucifer (cf. Suarez, De Angelis, lib. VII, xiii). As might be expected, the advocates of this view seek support in certain passages of Scripture, notably in the words of the Psalmist as they are cited in the Epistle to the Hebrews: "And again, when he bringeth in the first-begotten into the world, he saith: And let all the angels of God adore Him" (Hebrews 1:6; Psalm 96:7). And if the twelfth chapter of the Apocalypse may be taken to refer, at least in a secondary sense, to the original fall of the angels, it may seem somewhat significant that it opens with the vision of the Woman and her Child. But this interpretation is by no means certain, for the text in Hebrews 1, may be referred to the second coming of Christ, and much the same may be said of the passage in the Apocalypse.

It would seem that this account of the trial of the angels is more in accordance with what is known as the Scotist doctrine on the motives of the Incarnation than with the Thomist view, that the Incarnation was occasioned by the sin of our first parents. For since the sin itself was committed at the instigation of Satan, it presupposes the fall of the angels. How, then, could Satan's probation consist in the fore-knowledge of that which would, ex hypothesi, only come to pass in the event of his fall? In the same way it would seem that the aforesaid theory is incompatible with another opinion held by some old theologians, to wit, that men were created to fill up the gaps in the ranks of the angels. For this again supposes that if no angels had sinned no men would have been made, and in consequence there would have been no union of the Divine Person with a nature lower than the angels.

As might be expected from the attention they had bestowed on the question of the intellectual powers of the angels, the medieval theologians had much to say on the time of their probation. The angelic mind was conceived of as acting instantaneously, not, like the mind of man, passing by discursive reasoning from premises to conclusions. It was pure intelligence as distinguished from reason. Hence it would seem that there was no need of any extended trial. And in fact we find St. Thomas and Scotus discussing the question whether the whole course might not have been accomplished in the first instant in which the angels were created. The Angelic Doctor argues that the Fall could not have taken place in the first instant. And it certainly seems that if the creature came into being in the very act of sinning the sin itself might be said to come from the Creator. But this argument, together with many others, is answered with his accustomed acuteness by Scotus, who maintains the abstract possibility of sin in the first instant. But whether possible or not, it is agreed that this is not what actually happened. For the authority of the passages in Isaiah and Ezekiel, which were generally accepted as referring to the fall of Lucifer, might well suffice to show that for at least one instant he had existed in a state of innocence and brightness. To modern readers the notion that the sin was committed in the second instant of creation may seem scarcely less incredible than the possibility of a fall in the very first. But this may be partly due to the fact that we are really thinking of human modes of knowledge, and fail to take into account the Scholastic conception of angelic cognition. For a being who was capable of seeing many things at once, a single instant might be equivalent to the longer period needed by slowly-moving mortals.

This dispute, as to the time taken by the probation and fall of Satan, has a purely speculative interest. But the corresponding question as to the rapidity of the sentence and punishment is in some ways a more important matter. There can indeed be no doubt that Satan and his rebel angels were very speedily punished for their rebellion. This would seem to be sufficiently indicated in some of the texts which are understood to refer to the fall of the angels. It might be inferred, moreover, from the swiftness with which punishment followed on the offense in the case of our first parents, although man's mind moves more slowly than that of the angels, and he had more excuse in his own weakness and in the power of his tempter. It was partly for this reason, indeed, that man found mercy, whereas there was no redemption for the angels. For, as St. Peter says, "God spared not the angels that sinned" (2 Peter 2:4). This, it may be observed, is asserted universally, indicating that all who fell suffered punishment. For these and other reasons theologians very commonly teach that the doom and punishment followed in the next instant after the offense, and many go so far as to say there was no possibility of repentance. But here it will be well to bear in mind the distinction drawn between revealed doctrine, which comes with authority, and theological speculation, which to a great extent rests on reasoning. No one who is really familiar with the medieval masters, with their wide differences, their independence, their bold speculation, is likely to confuse the two together. But in these days there is some danger that we may lose sight of the distinction. It is true that, when it fulfils certain definite conditions, the agreement of theologians may serve as a sure testimony to revealed doctrine, and some of their thoughts and even their very words have been adopted by the Church in her definitions of dogma. But at the same time these masters of theological thought freely put forward many more or less plausible opinions, which come to us with reasoning rather than authority, and must needs stand or fall with the arguments by which they are supported. In this way we may find that many of them may agree in holding that the angels who sinned had no possibility of repentance. But it may be that it is a matter of argument, that each one holds it for a reason of his own and denies the validity of the arguments adduced by others. Some argue that from the nature of the angels mind and will there was an intrinsic impossibility of repentance. But it may be observed that in any case the basis of this argument is not revealed teaching, but philosophical speculation. And it is scarcely surprising to find that its sufficiency is denied by equally orthodox doctors who hold that if the fallen angels could not repent this was either because the doom was instantaneous, and left no space for repentance, or because the needful grace was denied them. Others, again, possibly with better reason, are neither satisfied that sufficient grace and room for repentance were in fact refused, nor can they see any good ground for thinking this likely, or for regarding it as in harmony with all that we know of the Divine mercy and goodness. In the absence of any certain decision on this subject, we may be allowed to hold, with Suarez, that, however brief it may have been, there was enough delay to leave an opportunity for repentance, and that the necessary grace was not wholly withheld. If none actually repented, this may be explained in some measure by saying that their strength of will and fixity of purpose made repentance exceedingly difficult, though not impossible; that the time, though sufficient, was short; and that grace was not given in such abundance as to overcome these difficulties.

The language of the prophets (Isaiah 14; Ezekiel 28) would seem to show that Lucifer held a very high rank in the heavenly hierarchy. And, accordingly, we find many theologians maintaining that before his fall he was the foremost of all the angels. Suarez is disposed to admit that he was the highest negatively, i.e. that no one was higher, though many may have been his equals. But here again we are in the region of pious opinions, for some divines maintain that, far from being first of all, he did not belong to one of the highest choirs--Seraphim, Cherubim, and Thrones--but to one of the lower orders of angels. In any case it appears that he holds a certain sovereignty over those who followed him in his rebellion. For we read of "the Devil and his angels" (Matthew 25:41), "the dragon and his angels" (Apocalypse 12:7), "Beelzebub, the prince of devils"--which, whatever be the interpretation of the name, clearly refers to Satan, as appears from the context: "And if Satan also be divided against himself, how shall his kingdom stand? Because you say that through Beelzebub I cast out devils" (Luke 11:15, 18), and "the prince of the Powers of this air" (Ephesians 2:2). At first sight it may seem strange that there should be any order or subordination amongst those rebellious spirits, and that those who rose against their Maker should obey one of their own fellows who had led them to destruction. And the analogy of similar movements among men might suggest that the rebellion would be likely to issue in anarchy and division. But it must be remembered that the fall of the angels did not impair their natural powers, that Lucifer still retained the gifts that enabled him to influence his brethren before their fall, and that their superior intelligence would show them that they could achieve more success and do more harm to others by unity and organization than by independence and division.

Besides exercising this authority over those who were called "his angels", Satan has extended his empire over the minds of evil men. Thus, in the passage just cited from St. Paul, we read, "And you, when you were dead in your offenses and sins, wherein in times past you walked according to the course of this world, according to the prince of the power of this air, of the spirit that now worketh on the children of unbelief" (Ephesians 2:1-2). In the same way Christ in the Gospel calls him "the prince of this world". For when His enemies are coming to take Him, He looks beyond the instruments of evil to the master who moves them, and says: "I will not now speak many things to you, for the prince of this world cometh, and in me he hath not anything" (John 14:30). There is no need to discuss the view of some theologians who surmise that Lucifer was one of the angels who ruled and administered the heavenly bodies, and that this planet was committed to his care. For in any case the sovereignty with which these texts are primarily concerned is but the rude right of conquest and the power of evil influence. His sway began by his victory over our first parents, who, yielding to his suggestions, were brought under his bondage. All sinners who do his will become in so far his servants. For, as St. Gregory says, he is the head of all the wicked--"Surely the Devil is the head of all the wicked; and of this head all the wicked are members" (Certe iniquorum omnium caput diabolus est; et hujus capitis membra sunt omnes iniqui.--Hom. 16, in Evangel.). This headship over the wicked, as St. Thomas is careful to explain, differs widely from Christ's headship over the Church, inasmuch as Satan is only head by outward government and not also, as Christ is, by inward, life-giving influence (Summa III:8:7). With the growing wickedness of the world and the spreading of paganism and false religions and magic rites, the rule of Satan was extended and strengthened till his power was broken by the victory of Christ, who for this reason said, on the eve of His Passion: "Now is the judgment of the world: now shall the prince of this world be cast out" (John 12:31). By the victory of the Cross Christ delivered men from the bondage of Satan and at the same time paid the debt due to Divine justice by shedding His blood in atonement for our sins. In their endeavours to explain this great mystery, some old theologians, misled by the metaphor of a ransom for captives made in war, came to the strange conclusion that the price of Redemption was paid to Satan. But this error was effectively refuted by St. Anselm, who showed that Satan had no rights over his captives and that the great price wherewith we were bought was paid to God alone (cf. ATONEMENT).