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4.5: Putting this into Practice: The Doctrine of Double Effect (DDE)

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  • Let’s consider some examples to show that what we have said so far might actually work. Imagine someone considering suicide. Is this morally acceptable or not? Recall, it is part of the Natural Law to preserve and protect human life. Clearly suicide is not preserving and protecting human life. It is therefore irrational to kill oneself and cannot be part of God’s plan for our life; hence it is morally unacceptable.

    Imagine that someone is considering having an abortion after becoming pregnant due to rape. The same reasoning is going to apply. We ought to preserve and protect human life and hence an abortion in this case is morally wrong.

    However, as we will see, Aquinas thinks that there are some instances where it is morally acceptable to kill an innocent person and therefore there may be occasions when it is morally acceptable to kill a foetus. But how can this be correct? Will this not violate the primary precept about preserving life? The answer is to understand that for Aquinas, an action is not just about what we do externally but is also about what we do internally (i.e. our motivations). With this distinction he can show that, for example, killing an innocent can be morally acceptable.

    To make this clear, Aquinas introduces one of his most famous ideas: the “Doctrine of Double Effect”. Let’s see how this works.

    Imagine a child brought up in a physically, sexually and emotionally abusive family. He is frequently scared for his life and is locked in the house for days at a time. One day when his father is drunk and ready to abuse him again he quickly grabs a kitchen knife and slashes his father’s artery. His father bleeds out and dies in a matter of minutes. Do you think the son did anything wrong?

    Many people would say that he did nothing morally wrong and in fact, some might even go as far as to say that he should get a pat on the back for his actions. What about Aquinas? What would he say?

    We might think that given the Natural Law to “preserve and protect life” he would say that this action is morally wrong. But, in fact, he would say the son’s action was not morally wrong (Aquinas discusses self-defence in the Summa Theologica (II–II, Qu. 64)).

    So why is the son killing the father not in direct contradiction with the primary precept? Aquinas asks us to consider the difference between the external act — the fact that the father was killed, and the internal act — the motive.

    In our example, the action is one of self-defence because of the son’s internal action and because of this, Aquinas would think the killing is morally acceptable. This distinction and conclusion is possible because of Aquinas’s Doctrine of Double Effect which states that if an act fulfils four conditions then it is morally acceptable. If not, then it is not.

    1. The first principle is that the act must be a good one.
    2. The second principle is that the act must come about before the consequences.
    3. The third is that the intention must be good.
    4. The fourth, it must be for serious reasons.

    This is abstract so let’s go back to our example. The act of the son was performed to save his own life so that is good — we can tick (1). Moreover, the act to save his life came about first — we can tick (2). The son did not first act to kill his father in order to save his own life. That would be doing evil to bring about good and that is never morally acceptable. The intention of the son was to preserve and protect his life, so the intention was good — tick (3). Finally, the reasons were serious as it was his life or his father’s life — tick (4).

    So given that the act meets all four principles, it is in line with the DDE and hence the action is morally acceptable, even though it caused someone to die and hence seems contrary to the primary precept of preserving life.

    We can draw a contrasting case. Imagine that instead of slashing his father in self-defence, the son plans the killing. He works out the best time, the best day and then sets up a trip wire causing his father to fall from his flat window to his death. Does this action meet the four criteria of the DDE? Well, no, because the son’s intention is to kill the father rather than save his own life — we must put a cross at (3).

    We have already seen that suicide is morally impermissible for Aquinas, so does that mean that any action you take that leads knowingly to your own death is morally wrong? No. Because even though the external act of your own death is the same, the internal act — the intention — might be different. An action is judged via the Natural Law both externally and internally.

    Imagine a case where a soldier sees a grenade thrown into her barracks. Knowing that she does not have time to defuse it or throw it away, she throws herself on the grenade. It blows up, killing her but saving other soldiers in her barracks. Is this wrong or right? Aquinas says this is morally acceptable given DDE. If we judge this act both internally and externally we’ll see why.

    The intention — the internal act — was not to kill herself even though she could foresee that this was certainly what was going to happen. The act itself is good, to save her fellow soldiers (1). The order is right, she is not doing evil so good will happen (2). The intention is good, it is to save her fellow soldiers (3). The reason is serious, it concerns people’s lives (4).

    Contrast this with a soldier who decides to kill herself by blowing herself up. The intention is not good and hence the DDE does not permit this suicidal action.

    Finally, imagine that a woman is pregnant and also has inoperable uterine cancer. The doctors have two choices; to take out the uterus and save the mother, but the foetus will die; or leave the foetus to develop and be born healthy, but the woman will die. What would Aquinas say in this instance? Well using the DDE he would say that it is morally acceptable to remove the cancer.

    The action is to remove the cancer; it has the foreseeable consequences of the foetus dying but that is not what is intended. The action — to remove the cancer — is good (1). The act of removing the cancer comes before the death of the foetus (2). The intention to save the woman’s life is also good (3). Finally, the reasons are serious as they are about the life and death of the woman and the foetus (4).

    So even though this is a case where the doctor’s actions bring about the death of the foetus it would be acceptable for Aquinas through his Natural Law Theory, as is shown via the DDE.

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