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The Relevance of the Heidelberg Theses today

The question of the legitimacy (or delegitimacy) of nuclear deterrence is once again one of the contentious and currently very relevant topics in ecclesiastical peace ethics. This is evidenced by the 2019 position paper of the German Commission Justitia et Pax, the synod of the Protestant Church in Germany that was held in Dresden in November 2019, and by the debates that took place as part of the “Orientational Knowledge on Just Peace” consultation process in recent years at the Protestant Institute of Interdisciplinary Research (FEST) in Heidelberg. The present article1 follows on from these debates. It serves as a counterweight to the current mainstream view within the Church, which clearly rejects the legitimacy of nuclear weapons and strategies. In this context, this article strengthens the complementarity concept contained within the Heidelberg Theses and links this concept to the fundamental idea of common security.

The strategy of nuclear deterrence has been highly contentious right back since the 1950s. Indeed, this issue almost caused a split in the Protestant Church in Germany. In the context of these disagreements, the aim at the time was “[staying] together under the Gospel”2. This was achieved by means of the so-called Heidelberg Theses (1959)3 – which were formulated by an interdisciplinary commission that was assembled at the Protestant Institute of Interdisciplinary Research (FEST) in Heidelberg as a result of an initiative by the Protestant Military Bishop Hermann Kunst.4

While nuclear deterrence was at the heart of political and church discourse in the era of the Cold War and the NATO Double-Track Decision, it has generally no longer been the focus of public attention over the last three decades. However, this now appears to be changing again. The nuclear issue has returned – also within the Church – particularly since April 2017, when the situation in North Korea escalated and the verbal exchanges between Kim Jong-un and Donald Trump were followed by both sides threatening to use nuclear weapons if a war started.

Ethical dilemmas, and possibly even “aporias”, arise in connection with nuclear deterrence.5 The primary question: Is it permissible to exercise a threat with weapons that must never be used? There are risks associated with the nuclear taboo, which persists through to the present day. These risks appear to have become greater since the end of Cold War bipolarity and the subsequent realignments in global politics. At the very least, the current geopolitical situation has become significantly more complex. With the two new geopolitical triangles of USA–Russia–China and China–India–Pakistan6, “new rivalries between major powers”7 have become evident, and China has assumed a new key position that has not been reflected upon to a sufficient extent even to the present day. At the same time, international arms control and disarmament efforts have reached a nadir and the nuclear option continues to be a component of military strategies. For example, the US Government’s 2018 Nuclear Posture Review even provides for the nuclear option as a response to non-nuclear threats.

Against this background, a Global Zero – a world without nuclear weapons – appears more urgent than ever. While this peace policy goal can be regarded as the consensus, the path to achieving it is a matter of debate. Is it time for churches to “unambiguously reject the moral legitimacy of nuclear weapons and strategies”, as formulated by Wolfgang Lienemann8? Or to put the question a different way, should the Heidelberg Theses, which were written 60 years ago as a peace ethics compromise solution to the nuclear issue, be regarded as obsolete?

The complementarity of the Heidelberg Theses as a compromise solution

Complementarity is a term borrowed from quantum physics. The physicist Nils Bohr (1927) used the concept of complementarity to describe the observed phenomenon that atomic particles have pairs of two coupled, but apparently contradictory properties. Carl Friedrich von Weizsäcker was instrumental in introducing this term in the context of peace ethics. In 1943, he stated in his book Zum Weltbild der Physik (“The World View of Physics”):

“In reality, Bohr appears to use the term complementarity to refer to something that is not confined to the specific case of quantum mechanics, but which occurs in all situations where a certain perspective prevents us from simultaneously looking in another direction and where this happens not by chance, but instead due to the inherent nature of the matter in hand.”9

The Heidelberg Theses (1959) make use of this term when stating the following:

“Thesis 6: We have to try to understand the various decision of conscience taken in the dilemma of nuclear weapons as complementary actions.

Thesis 7: The church must recognise that renouncing weapons is a Christian mode of conduct.

Thesis 8: The church must recognise that participation in the attempt to secure peace in freedom by the presence of nuclear weapons still remains a possible mode of conduct for Christians.”10 (Translations from German.)

This complementarity thesis, developed as a compromise solution, was intended to ringfence the contentious issues associated with the two mutually exclusive possibilities – keeping the peace through military means or by a complete renunciation of force – and to replace the “either-or” dichotomy with a “both-and” scenario. Deliberations on this matter can be found in the reasoning behind Thesis 11:

“In effect, each of the two positions that we have described underpins the other. In a very questionable manner, nuclear arms at least keep the arena open in which people such as rejecters of armaments, who enjoy civic freedom, can live in accordance with their convictions with impunity. However, we believe that these people, in a latent manner, help to keep open the intellectual space in which new decisions perhaps become possible.” (Translation from German.)

If the complementarity thesis initially related to the specific situation of nuclear deterrence, it was subsequently also applied in a general manner to the two fundamental positions regarding military force and to the decision to choose between military and civilian service. This rationale continued after the end of the Cold War. The document Schritte auf dem Weg des Friedens. Orientierungspunkte für Friedensethik und Friedenspolitik (“Steps along the path to peace. Orientation points for peace ethics and peace policy”) by the German Protestant Church (EKD) explicitly emphasises that the Church cannot exclusively advocate either military service or non-violent peace service. Instead, soldiers and conscientious objectors complement and justify one another:

“Soldiers need conscientious objectors and the peace services so that their actions are perceived as an expression of political responsibility by Christians and are not misinterpreted as resigned acceptance of this world; in turn, conscientious objectors and the peace services also need soldiers so that their actions are interpreted as a testament to Christian hope and are not misinterpreted as an expression of a lack of solidarity with the victims of violence and breaches of peace.”11

The 2007 peace memorandum by the Protestant Church in Germany (EKD) persists with this fundamental approach of “both-and” with regard to the legitimacy of military force, but no longer reasons with the mutual dependence of the two positions:

“The Christian ethos is based on a readiness to renounce violence (Matthew 5:38 ff.) and is primarily defined by the choice of non-violence. In a world that continues to be unredeemed and not at peace, serving others may also include the necessity of protecting rights and laws by using counter-force (cf. Romans 13:1-7). Both methods – that of renouncing force and that of military service – are preceded by conscientious, responsible decisions.”12

With regard to the question of the ethical legitimacy of nuclear deterrence, these two conflicting positions – nuclear pacifism, according to which “the threat of nuclear weapons can no longer be regarded as a means of legitimate self-defence”13, and the position that holds that “deterrence remains a valid principle”14 – also exist side by side in an unmediated manner. In this way, the fundamental concept behind the Heidelberg Theses of removing the antagonism between inherently incompatible positions is lost. This constellation in the memorandum by the German Protestant Church (EKD) is also lacking in terms of content: the two mutually exclusive positions and maxims are not free of contradictions and cannot be considered completely independently.

Ethical approaches to nuclear deterrence

Three fundamental positions can be identified in the discourse concerning nuclear deterrence in peace ethics:

“Use of nuclear weapons must always be wrong, and possession for deterrence must also be wrong.

Use might in some forms and circumstances be legitimate, and possession can therefore be justifiable.

While use must always be wrong, possession for deterrence can be justifiable.”15

In all three cases, there are critical questions to be answered: adherents to the first position must ask themselves how they justify leaving the use of nuclear weapons “as a one-sided option for the unscrupulous and the aggressive, unconstrained by countervailing power”16. After all, nuclear weapons have been developed and do exist. Hopes of achieving a world without nuclear weapons can be taken into account; however, this would appear to be a distant vision rather than a political reality within the context of current developments (such as the renaissance of geopolitics discussed above). The 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW) was not able to involve nuclear-weapon states and NATO states.

The second position is able to avoid the credibility problem of nuclear deterrence, but it is confronted with the problem of proportionality and the question of how the use of nuclear weapons can co-exist with the nuanced and proportional use of force. Even the development of so-called “mini-nukes” does not resolve the problem of proportionality, as the “collateral damage to the civilian population as a result of radiation from the contaminated radioactive fallout would still be immense”17 in the case of nuclear weapons with a low explosive power.

Adherents to the third position ultimately have to confront the dilemma of posing a threat using weapons that must never be used. Nuclear deterrence requires a sufficient degree of resolve to use the deterrent in critical situations. If the option to act in this manner is not available, the deterrent will not have any effect. This option is thus based on the tenuous assumption that “by consciously taking certain risks, the enemy can be encouraged to engage in a certain type of positive behaviour, and kept from carrying out specific actions”18.

The eighth Heidelberg Thesis of “securing peace in freedom through the presence of nuclear weapons” – even if this presence is not defined in further detail – can be assigned to the third position. Firstly, one could ask whether this approach has proven itself in practice in recent decades. The answer is an ambivalent one: on the one hand, the nuclear deterrent – notwithstanding all the uncertainties – has probably helped to prevent a nuclear war; on the other hand, it has not contributed to achieving progress on long-term disarmament. However, slowing of the dynamics of nuclear armament is possible in principle, even though favourable framework conditions are necessary; the INF Treaty and the New START Treaty serve as examples in this regard. Although the Non-Proliferation Treaty has not led to a long-term reduction in the nuclear potential of nuclear-weapon states and is often criticised for this, it has nonetheless helped to limit proliferation.

Nuclear deterrence in new global political constellations

How is the strategy of nuclear deterrence to be evaluated in the context of the current situation? The fundamental dilemma, the “double risk”19 – according to which the prevention of war by nuclear deterrence can fail, but a unilateral renunciation of nuclear weapons, or else the holding of nuclear weapons solely by autocrats or dictators can put peace in freedom at risk, continues to exist.

With the return of geopolitics, the strategy of nuclear deterrence appears to be experiencing a political renaissance. In this context, the new global political constellations that have emerged in recent years – whether these are more complex multipolar structures or the current military strategies of NATO and nuclear-weapon states – have undoubtedly lowered the inhibition threshold for the use of nuclear weapons and increased the risks of a nuclear war (including one triggered accidentally). The function assigned to nuclear deterrence – to prevent war – has become more fragile.

However, the converse is not necessarily true, i.e., that unilateral renunciation of nuclear weapons would reduce the probability of their use; instead, this option would also present a risk to peace. The latter might not apply to Germany. However, just imagine hypothetically that only countries such as North Korea or Russia were in possession of nuclear weapons: what about the freedom of countries with different understandings of values and order (such as the Western world), or of former Soviet republics that are now casting off the influence of Russia?

In addition, new technological developments – tactical nuclear weapons with lower explosive power that are associated with the potential to wage limited nuclear wars – have not led to a paradigm shift. On the one hand, the debate regarding the potential waging of limited wars is not new; since the 1950s, this has been the focus of strategic considerations.20 On the other hand, the technological ability to wage wars that are legitimate under international law, i.e. in accordance with the principles of proportionality and of distinction, continues to lie far in the future.21 Beyond this, a lot of compelling reasons continue to mitigate against (non-legitimate) waging of a limited nuclear war. For example, the risk of escalation of limited nuclear deployments – including those directed only at tactical targets – to the point of self-destruction continues to exist:

“Even if the war should be fought initially with so-called low-yield nuclear weapons, the losing side will always be tempted to redress the balance by resorting to weapons of greater power, thus inviting counterretaliation. Moreover, [...] limitations on the size of weapons to be employed cannot be enforced in practice, and each side will, therefore, seek to anticipate its opponent by using the largest practicable weapon.”22

A limited nuclear deployment would be extremely dependent on prerequisites, as both sides would have to have “access to reliable information on the intentions of the other side”.23 As a result, it does not just remain impossible, but above all, also undesirable for all sides, regardless of current military strategies.24

What conclusions can be drawn from this? Merely demanding the abolishment of nuclear weapons proves to be too simple. Giving up these weapons is not possible if this is not done in a multilateral manner. In addition, it can lead “to a complete reversal of cause and effect if nuclear weapons are identified as the cause of the danger instead of paying attention to the political causes of the conflict”25. This does not mean giving up the ambition of a world without nuclear weapons. However, one must differentiate between hope (even in the context of faith) and pragmatic political implementation. Peace is a process. The complementarity of the Heidelberg Theses is an expression of this. In this regard, the temporary nature of the word “still” contained in the Heidelberg Theses needs to be examined in further detail. It implies interim solutions. As criticised by Wolfgang Lienemann, these solutions should not be interpreted in such a broad manner that this “still” is “ultimately granted infinite validity for the duration of this fallen world”26. Instead, these solutions must be regarded as “part of a concept for political transformation”27. The “still” should be interpreted not just with regard to time, but also with regard to conditionality. Nuclear deterrence can be a “still […] possible” option, i.e. an ethically justifiable option, if it is linked with arms control and disarmament measures in order to get closer to achieving peace in freedom.

The Treaty on the Prohibition of Nuclear Weapons may represent an important signal in this regard, particularly within the context of complementarity in peace ethics, but it does not have political force without including the nuclear-weapon states and NATO states. In addition, Harald Müller, a leading peace researcher from Frankfurt, has observed: “The nature of this treaty does not represent significant progress relative to the Non-Proliferation Treaty and in certain details it is actually a step backwards.”28 For example, it opens up new loopholes “that appeared to have been closed with the Non-Proliferation Treaty and the resolutions of its review conferences (on the control of dual-use goods, for example)”29.

Outlook: Nuclear disarmament through common security

This article argues that the complementarity of the Heidelberg Theses, with the inclusion of nuclear deterrence, should be taken seriously. This does not negate the goal of banning nuclear weapons, but emphasises the process-based character of peace. Comprehensive steps in disarmament policy are associated with the expression “still” contained in the Heidelberg Theses. It will not be possible to do without the fundamental concept of common security. Indeed, the term itself already identifies the approach to a solution: we can no longer seek to achieve security from one another, we can only achieve it with one another.30 Today, this can no longer be limited to just the United States and Russia; multipolar structures require the involvement of all relevant actors. This makes common security more difficult to achieve, but there is no alternative to this. The risks associated with new technological developments and geopolitical constellations also point in this direction. Peace as a social phenomenon cannot be attained by a single – not even by a collective – actor; instead, it can only ever be achieved jointly. Confidence-building measures are particularly important in the context of the necessary arms control and disarmament. This approach is not new, but has been seriously neglected in recent decades – in internal church debate too – due to the focus on institutions for achieving liberal peace such as the EU and NATO. If long-term disarmament policy measures are to be successful, they must go hand in hand with the strengthening of cooperative structures and organisations such as the OSCE.

At the same time, disarmament must include gradual steps that are practicable for all states. With regard to nuclear disarmament, these steps could range from zones that are free of nuclear weapons, through to negative security guarantees31 and limitations to solely strategic nuclear weapons or minimal deterrents. In this area, new and alternative disarmament steps need to be developed that are capable of creating appropriate incentives even for nuclear-weapon states. We need to seek win-win situations. A Global Zero – the banning of nuclear weapons – is achievable only at the end of this path.

In addition, the implementation of common security is not just a task for political elites; it also requires efforts by all of society:

“Only if the concept of common security has become a common good and a mind shift of a few people has become a matter of course for many people will the masters have the necessary legitimacy for restructuring.”32

Churches have an important role to play here: in the cause of just peace, they can help to build confidence and promote a new culture of dialogue, and dialogue is most urgently required in those situations where it appears impossible.33

1 This article is based on Werkner, Ines-Jacqueline (2019): “Zur Aktualität der Heidelberger Thesen in der Nuklearfrage – ein Kontrapunkt.” In: Werkner, Ines-Jacqueline and Hoppe, Thomas (eds.): Nukleare Abschreckung in friedensethischer Perspektive. Wiesbaden, pp. 47–61. The author would like to thank Springer VS for granting the right to reprint this article.

2 Synod of the German Protestant Church in 1958, quoted from Härle, Wilfried (2011): Ethik. Berlin, p. 396. Translation from German.

3 Heidelberger Thesen zur Frage von Krieg und Frieden im Atomzeitalter (1959). Reprinted in: Erwin Wilkens (Ed.) (1982): Christliche Ethik und Sicherheitspolitik. Beiträge zur Friedensdiskussion. Frankfurt a. M., pp. 237–247.

4 The members of this commission included the physicist and philosopher Carl Friedrich von Weiz­säcker, the physicist Günter Howe, the theologists Helmut Gollwitzer, Karl Janssen, Hermann Kunst, Edmund Schlink and Erwin Wilkens, the historian Richard Nürnberger, the legal scholar Ulrich Scheuner, and the philosopher Georg Picht, who had been recently appointed as the head of FEST.

5 Rudolf, Peter (2018): Aporien atomarer Abschreckung. Zur US-Nukleardoktrin und ihren Problemen. Berlin.

6 cf. Rudolf, Peter (2019): “Zur Politik und Ethik nuklearer Abschreckung unter veränderten internationalen Bedingungen.” In: Werkner, Ines-Jacqueline and Hoppe, Thomas (eds.): Nukleare Abschreckung in friedensethischer Perspektive. Wiesbaden, pp. 85–104, p. 87.

7 Rudolf, Peter (2018): US-Geopolitik und nukleare Abschreckung in der Ära neuer Großmachtrivalitäten. Berlin.

8 Lienemann, Wolfgang (2019): “Zur Aktualität der Heidelberger Thesen in der Nuklearfrage.” In: Ines-Jacqueline Werkner and Thomas Hoppe (eds.): Nukleare Abschreckung in friedensethischer Perspektive. Wiesbaden, pp. 13-46, p. 38. Translation from German.

9 Weizsäcker, Carl Friedrich von (2002 [1943]): Zum Weltbild der Physik. 14th edition, Stuttgart, p. 331. Translation from German.

10 Translation of theses 6 and 8 according to; thesis 7 translated from German.

11 Evangelische Kirche in Deutschland (EKD) (1994): Schritte auf dem Weg des Friedens. Orientierungspunkte für Friedensethik und Friedenspolitik. Hanover, pp. 23f. Translation from German.

12 Evangelische Kirche in Deutschland (EKD) (2007): Aus Gottes Frieden leben – für gerechten Frieden sorgen. Eine Denkschrift des Rates der Evangelischen Kirche in Deutschland. Gütersloh, No. 60. Translation from German.

13 Evangelische Kirche in Deutschland (EKD) (2007): Aus Gottes Frieden leben – für gerechten Frieden sorgen. Eine Denkschrift des Rates der Evangelischen Kirche in Deutschland. Gütersloh, No. 162. Translation from German.

14 Evangelische Kirche in Deutschland (EKD) (2007): Aus Gottes Frieden leben – für gerechten Frieden sorgen. Eine Denkschrift des Rates der Evangelischen Kirche in Deutschland. Gütersloh, No. 164. Translation from German.

15 Quinlan, Michael (1989): “The Ethics of Nuclear Deterrence: A Critical Comment on the Pastoral Letter of the U.S. Catholic Bishops.” P. 3.

16 Quinlan, Michael (1989), p. 4.

17 Barleon, Leopold (2012): “Heben Mini-Nukes die Singularität auf?” In: Eisenbart, Constanze (Ed.): Die Singuläre Waffe. Was bleibt vom Atomzeitalter? Wiesbaden, pp. 129–141, p. 141. Translation from German.

18 Senghaas, Dieter (1981): Abschreckung und Frieden. Studien zur Kritik organisierter Friedlosigkeit. 3rd edition, Frankfurt a.M., p. 124. Translation from German.

19 Lienemann, Wolfgang (1982): “Geschichte und Zukunft der Komplementarität.” In: Aktion Sühnezeichen/Friedensdienste (Ed.): Christen im Streit um den Frieden. Freiburg, pp. 169–177, p. 172.

20 Kissinger, Henry A. (1984 [1957]): Nuclear Weapons and Foreign Policy. Boulder, CO, pp. 174 ff.; Schmidt, Helmut (1961): Verteidigung oder Vergeltung. Stuttgart, p. 124.

21 cf. Altmann, Jürgen (2019): “Neue Typen von Kernwaffen und ihren Trägern. Gefahren für die strategische Stabilität.” In: Werkner, Ines-Jacqueline and Hoppe, Thomas (Eds.): Nukleare Abschreckung in friedensethischer Perspektive. Wiesbaden, pp. 105–123.

22 Kissinger, Henry A. (1984), p. 174 f.

23 Kissinger, Henry A. (1984), p. 178.

24 Kissinger, Henry A. (1984), p. 175.

25 Nerlich, Uwe and Rendtorff, Trutz (1989): “Einleitung der Herausgeber” (Introduction by the editors). In: ibid. (Eds.): Nukleare Abschreckung – Politische und ethische Interpretationen einer neuen Realität. Baden-Baden, pp. 19–53, p. 36f. Translation from German.

26 Lienemann, Wolfgang (1982), p. 173. Translation from German.

27 Nerlich, Uwe and Rendtorff, Trutz (1989), p. 34. Translation from German.

28 Müller, Harald (2018): “Der Nukleare Nichtverbreitungsvertrag und der neue Kernwaffenverbotsvertrag – harmonisch, kompatibel, unverträglich?” In: Sicherheit und Frieden, 36 (2), pp. 61–66, p. 66. Translation from German.

29 Müller, Harald (2018), p. 65.

30 cf. Schubert, Klaus von (1992): Von der Abschreckung zur gemeinsamen Sicherheit. Baden-Baden, p. 161.

31 This refers to a guarantee not to attack non-nuclear-­weapon states with nuclear weapons.

32 Schubert, Klaus von (1992), p. 164. Translation from German.

33 cf. Reißig, Rolf (2008): “Weltgesellschaft – Dialog- und Transformationsprojekt des 21. Jahrhunderts.” In: Bahr, Egon (Ed.): Weltgesellschaft. Ein Projekt von links! Berlin, pp. 21–40, p. 34.


Ines-Jacqueline Werkner

Ines-Jacqueline Werkner is Head of Peace Research at the Protestant Institute for Interdisciplinary Research (FEST) in Heidelberg, and a lecturer in the Institute of Political Science at Goethe University Frankfurt. She studied social sciences at the Humboldt University of Berlin, and gained her doctorate and habilitation in political science at Freie Universität Berlin. She has worked at the European University Center for Peace Studies in Stadtschlaining/Austria and has held various visiting professorships (Vilnius, Kiel, Lucerne).

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All articles in this issue

The End of the "Interlude" – Nuclear Deterrence in the Light of Roman Catholic Social Teaching
Heinz-Günther Stobbe
Waiting for Armageddon: Theological and Ethical Aspects Of Nuclear Deterrence
Drew Christiansen SJ
The Relevance of the Heidelberg Theses today
Ines-Jacqueline Werkner
Exposing Flaws in the Logic(s) of Nuclear Deterrence as an International Security Strategy – a Feminist Postcolonial Perspective
Madita Standke-Erdmann, Victoria Scheyer
We Are the Bomb: Opaque Financial Flows and Unwitting Involvement in Nuclear Armament
Robin Jaspert
Extended Nuclear Deterrence and Participation: Overcome Together, Don’t Go It Alone
Wolfgang Richter
Nuclear Arms Control, Disarmament and Nonproliferation Regimes in Deep Crisis
Tom Sauer
"No Way Out": Nuclear Weapons Remain An Important Factor in International Politics
Michael Rühle
Russian Nuclear Weapons: Reason or Feelings?
Konstantin Bogdanov
China’s Nuclear Strategy in a New Geopolitical Environment
Sven Bernhard Gareis


Markus Bentler Burkhard Bleul