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What is Evil? Aquinas’ Classical Definition Found in Catechism

February 20, 2014 by  
Filed under Demonology, Evil, Fr. Fortea

What is Evil?

Aquinas, Thomas Aquinas, Aquino, St Thomas AquinasFather Fortea, what is evil?

Evil is the lack (or privation) of a good that should be present in a thing. For example, blindness is a physical evil because it is the absence of the ability to see, which is proper to a human being. In moral terms, sin is the absence of a particular virtue in a person. As such, evil is not something that exists in itself; it is merely the absence of the good (see Catechism of the Catholic Church paragraphs 309, 314).


This classical definition, formulated by St. Thomas Aquinas in the thirteenth century, was the result of centuries of thought and the refinement of complex formulas into this simple, objective explanation.



Editor’s Note:  To learn more about spiritual warfare and demonology, Catholic Spiritual Direction recommends Fr. Fortea’s excellent book, Interview With An Exorcist – An Insider’s Look at the Devil, Demonic Possession, and the Path to Deliverance.


Art: Thomas von Aquin [The formulator of the definition of evil: Thomas Aquinas], Sandro Botticelli (1445-1510), unknown date, PD-US published in the U.S. prior to January 1, 1923, author's life plus 100 years or less, Wikimedia Commons.

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About Fr. Jose Antonio Fortea

Father José Antonio Fortea is not only an exorcist, but also a writer, and parish priest. He once thought he would lead what he has termed ordinary life as an attorney in Madrid, much as his father did before him, but sensed instead a vocation to the priesthood in his adolescent years. A theology graduate of Navarre University in Spain, Father Fortea wrote a thesis there on exorcism. He has been a practicing exorcist for several decades.

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  • byonan

    The stipulation that “sin is the absence of a particular virtue in a person” does not seem adequate. First, moral evil or sin is a privation. It is a privation of conformity to right reason and to the law of God. The morality of a human act consists in its agreement or non-agreement with right reason and the eternal law. When the intelligent creature, knowing God and His law, deliberately refuses to obey, moral evil results. (See Catholic Encyclopedia (1913) article “Sin.”

    Second, and here is my point, sin does not necessarily involve “the absence of a particular virtue.” This can be seen by considering venial sin. For example, a person may have all the virtues but commit a venial sin such a telling a lie. A venial sin does not deprive the soul of sanctifying grace, or diminish it. It does not produce a “macula,” or stain, as does mortal sin, but it “lessens the luster of virtue.” On this point see Aquinas, “Summa Theologiae,” I-II Q. 89 art. 1.

    • judeen

      telling a lie ,is a mortal.. sin…. seprating us from God and His protection…. virtues are weak and can be strong.. we have protection from God when we are pure and right with Him… this is even worn off by venial sins… that is why we say the OH my God prayer…. every day to stay right with God and Gods power dwelling in us and all around us

      • LizEst

        judeen–To be sure, telling a lie is a sin. But, whether or not it is a mortal sin depends on the seriousness of it. Venial sins weaken us and dispose us to committing more serious sins. So, even venial sins are not acceptable since they distance us from God.

        God bless you and keep you, judeen.

        • judeen

          Your so right… one needs the 3 things to commet a mortal sin.. brought up that if one steals a penney it is a sin… for it was not mine. and also that person might need the penny more and could be very serious to them…. to strict.. ya.. I am… knowing how we hurt our selves by making sin light or forget it and how it hurts God and others….. sorry

        • Karen Guilford

          Telling a lie is not always a sin. Thomas Aquinas goes into great detail in teaching about this. It’s the intention behind the lie. It’s a matter of the heart. If I can find Aquinas’ quote I will post later.

    • byonan

      My point is that if a venial sin “lessens the luster of virtue”, then it is incorrect to define sin as “the absence of a particular virtue in a person.”

      • $1650412

        I think if you consider it by degrees, which is what we are doing when we talk about venial sin and human weakness, it makes sense. In venial sin maybe for the sake of illustration- we have not gouged out a hole in virtue so to speak but we have definitely shaved some depth off the building block there, or picked at the surrounding cement or in some other way of marred the integrity of the whole in terms of strength, beauty, and function.

  • Karen Shields Wright, MS, DC,

    Fr. Fortea, I disagree with your example here for evil, even from a purely philosophical discussion: “For example, blindness is a physical evil because it is the absence of the ability to see, which is proper to a human being.” Absence of an ability to see from a spiritual standpoint I can take as leading to evil or as evil, yet in the physical state, blindness or other disabilities or diseases should not be classified as evil. I can agree eyesight is proper to the human body and beneficial, yet to state it falls into the category of evil is implying an ideological foundational principle of believing in the perfection of the human body in the here and now. Such implication takes us down the slippery slope into what we have today, the idolatry of the body as we see all over our media today. Physical blindness and other physical maladies has existed since the fall of man, and should not be equated with terms such as sin or evil. For sin and evil applies to moral terms. Physical blindness is an amoral condition.

    • Camila

      Hi Karen, So will the blind not be healed from his physical malady in the resurrected body? You wouldn’t call ‘physical maladies’ ‘physical evils’?

      You say “Physical blindness is an amoral condition” I agree, I believe that’s why Fr.Fortea called it a ‘physical evil’ not a ‘moral evil’.

      • I hope this means I’ll actually be a good singer in my resurrected body! :))

        • Camila

          Oh Mary, absolutely! I sure hope we’ll be joining the nine Choirs of angels in the singing and praising of God!!! If we are called to sing while on earth, all the more will we sing in heaven!!!!

          “All the earth falls in worship before you;
          they sing of you, sing of your name!” (Psalm 66:4)

          • Thanks! Sounds great! An eternity singing His praises! 🙂

          • MarcAlcan

            Oh Mary, absolutely! I sure hope we’ll be joining the nine Choirs of angels in the singing and praising of God!!

            Don’t we already do that at Mass?

            And so, with Angels and Archangels, with Thrones and Dominions, and with all the hosts and Powers of heaven, we sing the hymn of your glory, as without end we acclaim:

            Holy, Holy, Holy Lord God of hosts.
            Heaven and earth are full of your glory.
            Hosanna in the highest.
            Blessed is he who comes in the name of the Lord.
            Hosanna in the highest.

            As Scott Hahn’s book says – the Mass is heaven on earth.

        • judeen

          ask now if you want to … to bless your voice and the angels sing with you… and watch your voice become beautiful we do not have to wait until dead and ressurected to receive a gift from God….

          • Thank you! Will try praying for it! 🙂

          • judeen

            may God bless your voice ,, !!

          • Camila

            Great idea!

    • judeen

      Jesus talks about physical illments . and why people have them , some are from the sin of generations past.. some are from our own sin… yet others , it is for the glorification of God… and yet I too think .. some are joined with the passion of our Lord to suffer for other souls… when God takes something away , something replaces it.. the hearing and touch and spiritual senses become alert and stronger than a normal persons… there is many reasons for illness… strenghten faith in others or our selves… people turn from sin… knowing God is important and we need Him so on…
      evil … is the lack of God… in anything… also there is spiritual evil… that is the fallen angels.. know that they are real.. and those who have the gift can see them as well as Gods angels.. and the orras around people ….

      • Jeanette


      • judeen

        reply- truth is truth.. and I am not educated.. as you can see in my spelling.. I have expereinced alot… spiritually.. bragging.. no .. I get angry over people educated and do not look for the spiritual side of things… and think they understand things when they have not expereinced things… do you call peter on the sidewalk bragging? trying to tell all about Jesus? I would say not.. the spirit led him to tell the world of Jesus power… and promises… and what he expereinced.I put a comment on my own to explain how I know.. some things.. I also know what it is like to have generational sin.. and how hard it is to stop it…

    • $1650412

      Karen, I totally understand what you are saying- but I think there are two things working here. One is the objective reality that every defect in nature is due to the work of evil by the infiltration of original sin. So every thing that is a result of a deformed creation because of sin in the world- can be attributed to evil- objectively speaking.
      We also know however, that Jesus said with regard to this same specific ailment- in the case of the man born blind that it was not because of his sin, or the sin or his parents, but for the glory of God- So while we have to acknowledge that all of the created order is corrupted by sin, and death which was never natural to Earth and life on earth, has become the inescapable swallowing vortex toward which all things tend. That is the primary result of evil – or it is evil itself because it is the ‘fruit’, if you will. So the remedy, Jesus Christ’s incarnation, passion death and resurrection have been plunged into the heart of this ‘thing’ and as grace permeates the whole, evil is undone and creation is renewed- but it is a work that goes through time and space, past and present, reaching toward and into the future and eternity when all creation will be resurrected in Christ. So, the imperfections defects, weaknesses, and absences of what God originally intended, especially in the physical nature of human persons is being undone by grace and there is a time coming, a day when we will experience the glorification of our whole selves because we ‘see Him as He is’, we will be like Him.
      This is why our witness to the value of EVERY human person is so critical to our time- it is the most powerful testimony to the virtue of hope. We don’t value people according to utility, or how well they might seem to fit with our concept of order and beauty- although those ideals are qualities of God and He has blessed them. And we do not deny the reality of evil or sin or death of chaos or entropy – damage is done. The truth is that we are all moving toward the day and the state in which all that is a vacuum for good right now will be completed. We will do what we can to fill everything with grace and on that ‘day’ God will be glorified and magnified most brightly in those places where grace is ‘purest’ or worked most powerfully. He works together all things for the good of those He loves and has called according to His purpose. Romans 8:28.
      Back to your point, never at any time should a person’s moral value be judged by his or her physical condition- always and everywhere we should see every beauty and grace as it is- a reflection of God and His love; and every hurt and defect as a place where an even greater grace might magnify the Lord now and in eternity, giving supernatural witness to hope.

      • Karen Shields Wright, MS, DC,

        Jo, I understand completely your thoughts here and appreciate the depth you reached in presenting the reality of the grace that is given to us through Christ.

  • judeen

    you do not beleive in the devil do you? what do you say about the scriptures that talk about the devil? tempation of Jesus, Jesus said that the devils like each other but christian will love even their enemys.. or the fallen angles cast out of heaven… if you worked with people possed , you would have a very different out look

  • Pop

    What a surprising answer. It seems to imply that privation entered
    the swine that ran over the cliff subsequent to the exorcism of Legion; that
    Paul (Acts 16) cast out clairvoyant privation, and that Christ’s temptations in
    the desert were due to the privation of food, drink and companionship and
    nothing more. Paradise as well must have
    included privation sufficient to have caused Eve’s demise. And it is privation that prowls the
    world, accuses good folk and lies. The warfare Paul speaks of in Ephesians
    then is warfare against an enemy who is absent … beyond absence, of course.
    How should one understand these scripture
    passages thereby?

    One would then conclude that the levitations of
    the folk and the Febreze bottle mentioned in the article on
    exorcism at this website were due to the privation of gravity and


    • $1650412

      There is an interesting meditation there and I think you should ask the Lord more about Newton’s laws as you consider this as a way of understanding these things, but be careful that you do not try to impose a method of ‘human understanding’ onto a supernatural reality in an attempt to box it in in some way. We are talking about fallen angelic beings, their actions, and the side effects via human accomplices- this has aspects of mystery we cannot define or understand- THANK GOD! I don’t know how they/it do what they do- especially when it seems to manipulate nature- but we do know it happens. St. Anthony of the Desert and St. Padre Pio both did combat with the devil with physical manifestations and sufferings- I think that is scary. But, every Christian must understand and be strong in self-denial and mortification for love of Christ, because this is what gives us the supernatural power to withstand every firey arrow and every demonic blow, and the courage to know how to pray when we have to deal with this- these are skills necessary to spiritual survival in our time.

  • Mark DeLaurentis

    Dear Father, on Nov 21, 2013 you answered this question in the affirmative

    Q. Father Fortea, does evil really exist? A. Yes, it does. The first thing we need to know is that evil – like good – is an objective reality.

    Read more:

    How then is Evil a privation?

    Aquinas is The Man

    but he is after all…..a man

    • Mark – we don’t have the blessing of Fr. Fortea’s responses to combox questions. You will have to work it out with the resident theologians. The Catechism is the best place to start.

    • $1650412

      Here is my understanding of this. In that previous conversation, I think Father Fortea’s orientation was to explain there is a definitive personal reality (or a bunch of them) who is our enemy. The devil and his minions are not a force, or substrata of the universe- they are personal spiritual beings, each one originally, uniquely created by God to give Him glory. But, through rebellion and crimes against God, themselves, the created order and most of all the human race- they have become a entity of evil. Each one is an agent of wickedness, and their individual and collective missions are to lie, steal, kill, and destroy. We refer to them as one or many, the devil, the adversary, Satan, the enemy etc. (I am not sure but I think they have a hierarchy, and they function like a government or an army of sorts without anything remotely associated with virtue like loyalty or obedience or fidelity to a cause- I don’t want to think about it much, but that is the general observation I have of all that.) We have to be careful how much air time or thought time we give this stuff – because it is a means of temptation. Moving on-
      My take on this present topic. Evil, the thing, (the side effect of the work those guys above are engaged in) should not be evaluated on its own merit by definition- it is a relational aspect of a greater reality- it only exists as an absence of good. The most that the enemy can do is fragment and disperse, in order to divide, for the sake of making ‘gaps in the good’ if you will. I think of chaos and entropy.
      One way we might think about it is if we were to ‘pixilate’ the fabric of our souls, or our being, our relationships, our life, work or experiences- the enemy is attempting to erode the pixels of you soul, or to break them apart from the whole- to drag pieces of you away to dark separated places or into other disordered configurations. He will attempt to get us to rearrange ourselves like a bad version of a broken rubic’s cube- or distract us from the ways in which we are created to bringing order, beauty, harmony, love and peace back into our lives in Jesus through conforming one step at a time to the order and union that He Himself is for us, as the God/Man in the Most Holy Trinity.
      The best counsel, as a follow on to this idea of ‘places’ where there is ‘no good’ – is that we live to counter evil with good. Bring virtue where it is lacking- where there is not love, be loving, where there is weakness in Christian discipline, live a prayerful ordered life- (see the Benedictine Rule and go one prayer/duty at a time); where hope is flagging and joy is unknown, be light and salt by acts of mercy. And lastly, St. Paul considered himself an oblation poured out in love and service Philippians 2:17- like wine poured out in sacrifice to God. Wine being a liquid is going to fill in all the places it runs to- sacrifice will fill in the gaps when the force of repairing recontstructing and reorder alone cannot completely undo the damage or restore the fragmentation the enemy wreaks. Being ‘poured out in love’ will go even further in the Power of the Holy Spirit to cover a multitude of sins. At least that is what I understand to be the case.

  • Willie Simpson

    The classic definition is concise, but would be nice if it contained more explanation; as an active spiritual force that found embodiment in Satan and associated influences. One of the most subtle is the movement it finds in the human condition based in self authority (self enthronement). All blessings to F. Fortea and The church:-)

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