Areas of Specialization

1.  Practical philosophy:
1.1. Ethics: 1.1.1. metaethics: justification of morals, moral semantics, motivation for moral action; 1.1.2. normative / material ethics: criteria of morality, in particular of justice; moral desirability, moral duties; 1.1.3. applied ethics: environmental ethics, future ethics, bioethics, economic ethics, developmental ethics, ethics of sports.
1.2. Theories of rational action: 1.2.1. rational decision theory and game theory: 1.2.2. prudential desirability functions; 1.2.3. theories of the good life.
1.3. Philosophical anthropology: 1.3.1. philosophy of action: empirical laws of action, empi­rical theory of decision, concepts of action and intention, freedom and responsibility; 1.3.2. theory of emotion and feeling; 1.3.3. moral psychology; 1.3.4. happiness and well-being.
1.4. Other areas of practical philosophy: political philosophy.

2.  Theoretical philosophy:
2.1. Theory of argumentation (with strong components in logic and epistemology).
2.2. Metaphilosophy: types of theories in philosophy.

Areas of competence

2.3. Philosophy of language.
2.4. Philosophy of science: induction, interpretation.

3.  History of philosophy: Kant, Hume, Aristotle.


I teach in German, English and Italian. I also read French, Spanish and Latin.

Some research questions and results

With respect to contents, some of the main philosophical questions I am primarily interested in are:

  • moral criteria in general and criteria of justice in particular, as well as the application of these criteria to social, political and economical systems;
  • happiness, criteria of the good and of prudential rationality, the good life;
  • criteria and methods of acquiring knowledge of all types.

However, my inquiry into these questions is strongly shaped / characterised by two features, first, the attempt to provide positively useful knowledge and, second, a methodical approach together with the attempt to provide strong justifications. As a consequence, I have dedicated much research to questions of what philosophical theories and methods are, to criteria of knowledge and justification, in particular in ethics, and to acquiring as well as philosophically theorising empirical information which is needed for developing other desired philosophical theories. The following (of course incomplete) presentation, however, does not reflect this systematic order, rather, it highlights some paradigmatic questions and results in a personal order. It contains references to some of my publications, and uses scribal abbreviations which are decoded in the list of publications.

            Normative ethics: My research in normative ethics (or more precisely: criteriological ethics) is about the criteria and sources of morality, in particular criteria of social justice.
Basic approaches in normative ethics: I have defended an axiological approach in normative ethics, i.e. an approach which takes values to be primary with respect to obligations or virtues and hence defines deontic and aretic notions via axiological notions and not vice versa (sometimes this approach is erroneously called “consequentialism”). This differs from the deontological and the virtue approaches, which take obligations and virtues respectively to be primary. [A62.]
Axiology: moral desirability function: In the axiological part of normative ethics I have developed, in particular, a prioritarian criterion of moral value (called “utilex”), i.e. a criterion, which, unlike utilitarianism, gives more moral weight to improvements for people who are worse off, more weight the worse off they are, thus operationalising greater concern for these people [B2: 589-632; A32; A66; A77]. Technically, this is  done by translating the personal value of a life into a moral value of this life via a concave weighting function, the “utilex” function. On this website, this weighting function has been used as a kind of logo: : the x value expresses the personal desirability of a life; and the corresponding y value is the moral value of this personal desirability.
Justification of the moral desirability function: I have justified this criterion via a model of our expected sympathy for people one is not personally acquainted with, where negative sympathy, i.e. compassion, is stronger than positive sympathy – which leads to the concavity of the moral desirability function [B2: 589-616; A32; A66; A77].
Deontology: moral obligations: The prioritarian utilex criterion is about moral values. In addition, I have developed a criterion of moral obligation: norm progressivism, which relies strongly on socially valid norms and the political process of, in the best case, implementing the morally most efficient new norms, thereby morally improving the world in a long-term historical process. Basic moral obligations consist in abiding by the morally good socially valid norms. [B3: 85-88; 93-97.]

Ethical methodology and criteria for justifying morals:
The main focus of my research in metaethics is criteria for good justifications of moral systems and of practical justifications (or practical reasons) in general. An important adequacy condition for practical justification is a certain kind of internalism: While the practical justification, on the one hand – like theoretical justification – has to prove or argumentatively justify a certain thesis about the justified object, on the other, as a practical justification, it must have a motivating function. In other words, belief in this thesis motivates prudent people – to a certain degree – to adopt and practically realise the justified object. Because motivating is a causal relation, this internalist adequacy condition makes a theory of practical reasons dependent on motivational psychology and empirical decision theory. A deeper elaboration of this internalism leads to an instrumentalist conception of morality. [B2: 30-127; A20; A38.2; A41; A73; A74; A78.]
Moral semantics and sources of morality: This solution for the problem of practical justification implies a certain kind of moral semantics, namely a combination of semantic cognitivism, which means that moral judgements should be defined in such a way as to have clear and interpersonally verifiable or at least checkable truth conditions, and adoptive non-cognitivism, which means that practically adopting moral criteria is not a question of cognition alone but depends on – innate – motives too. Moral judgements should be defined in such a way that this adoption is guaranteed; for prudent subjects the adoption of justified morals should be a question of prudential rationality. [A18; A46.2; A55; A73.]

            Applied ethics:
Climate ethics:
The biggest portion of my research in applied ethics so far has been dedicated to environmental ethics, and to climate ethics in particular. In a preliminary study, I have assessed various options with respect to greenhouse gas emissions with an entirely welfare ethical methodology; whereas economists assess such options in monetary terms (sometimes including substitutive monetisation for goods without market prices), welfare ethics does it in terms of personal utilities, which then are aggregated, according to the respective ethical criterion, e.g. prioritarianism or utilitarianism. (Insofar as I am aware, my study is the only welfarist assessment study of greenhouse gas emission options to date.) Sustainable reduction of emissions turned out to be the morally best option, according to both prioritarian and utilitarian criteria. [B3; A52 – further topics: A91.]
Developmental ethics: Developmental ethics deals – directly or indirectly – with the problems of the, by far, biggest group of humans living in destitution; and many people believe that, apart from feeling moved by these circumstances, it is also a matter of justice that the relatively rich should – more or less massively – help the poor. One part of my research projects in developmental ethics consists in trying to provide theoretical underpinnings for these thoughts [cf. above]. The criterion of moral obligations intimated above requires that new social norms be established for moral reasons where this is morally most efficient. The situation of the destitute fulfils this condition for several reasons: moral priority as well as high marginal utility because of their miserable condition; often low costs because of purchasing power parity; and misery due to lack of simple technical means, which could quite easily  be provided by the more affluent. [A103.]
Further areas of applied ethics: I have contributed to some other fields of applied ethics: general environmental ethics [A34], future ethics [A60], bioethics [A61; A92], economic ethics [A51], ethics of war [A88], ethics of sports [A26].

            Theory of rational action / prudential reason:
Desirability theory:
Arguably, the best theory of rational utility or prudential desirability so far is the full information approach, developed in particular by Richard Brandt. However, this theory has several crucial problems, which mostly originate specifically from the full information requirement (e.g. since we do not know how we would decide with full and vividly represented information this approach is of no practical help). Therefore, I have developed an analytic-synthetic theory of prudential desirability, which avoids these problems and conserves the advantages of the full information approach. The basic idea is to analyse the various ways of how we can decide and to take the best of them as defining rational preferences – where “the best” is understood as being resistant to further information. In this way, the procedural definition of ‘desirability’ and the question of further psychological and situational information about our ways of deciding are separated. [B2: 241-427; A18; A21.]
Intrinsic values: With the help of these criteria and of empirical information about our ways of deciding I have defended a certain type of rational hedonism (“corrected hedonism”) as the right theory of intrinsic values. [B2: 428-548; A31; A35.]
Rational decision: Rational decision is neither simply choosing the option believed to be best – this is what we do necessarily in any case, and it does not guarantee a minimum of information or other quality of the decision –, nor, at the other end of the spectrum, does it consist in always trying to obtain the maximum of information about the available options – thereby ignoring the costs and benefits of this information. As an alternative to these extremes, I have developed a theory of rational decision as optimal decision process: Apart from the quality of reflection (good criteria and their coherent application), the other major variable of different ways of deciding is the invested effort, measurable for example, in terms of time dedicated to finding better alternatives, relevant consequences etc. Improving these two aspects of a decision (quality and effort) will lead to choosing better options. However, the marginal benefit of these improvements usually diminishes, so that there is an optimum level of decisional effort and quality, i.e. a maximum of the sum of the utilities of the decisional effort and of the chosen option itself. It is rational to decide on this optimum level. We can learn to invest this optimum level of deliberation with the help of statistically justified rules of thumb. [A1: 390-404.]
Theory of the good life: According to the theory of intrinsic value, a good life is a (certain kind of) happy life. Psychology of well-being can help tell us which kind of life will make us happy. In particular, I have stressed two of its results, which are highly important for ethics: Higher income makes us happier, but only up to a certain degree (in the US: 75,000 USD/year, according to Kahneman & Deaton); beyond that level its contribution to happiness is nil. Altruistic action is a very stable source of happiness. [B2: 549-576.]

            Theory of action: My contributions to action theory have been threefold.
Empirical theory of action: My empirical theory of action tries to systemise psychological findings about our ways of deciding and acting, in the form of a limited set of coherent hypotheses which should be able to explain or describe every part of a decision and which should capture the various ways of deciding and in particular whether these depend on special cognitions. This systematisation provides the empirical foundation for the prudential desirability theory, the theory of rational decision and for ethics, i.e. for all “normative” theories of practical reasons. In particular the systematisation clarifies which ways of deciding can be accessed by acquiring certain knowledge. Without such a psychological or action theoretical foundation the normative theories cannot give useful advice which can be followed. Important parts of this empirical theory of action include the hypothesis that intentions are optimality judgements, hypotheses about the hedonic and other content of our intrinsic desires, a theory of emotional decisions, as well as explanations of the motivational and cognitive bases of our moral actions. [B2: 128-240; 428-521; B4; A35; A48; A56; A67; A100.]
Reconstructive action theory: A methodically different part of my philosophical action theory is dedicated to clarifying concepts such as ‘action’, ‘intention’, ‘intentional’. The guiding idea behind the resulting definitions is that these concepts have to capture what is valuable and of high practical importance among the natural phenomena in the respective fields. One example for implementing this idea is the definition of ‘intentional’, where understanding why deviant realisations of intentions are bad in at least one respect – namely that they run counter to the idea of control inherent in the concept of action – is the key to resolve this persistent definitional problem. [A48; A75; A84.]
Freedom and responsibility: Still another and methodically different part of my action theory is about freedom and responsibility, where I defend a compatibilist conception of freedom as, in its highest form, convergence of prudential rationality and autonomy. Whilst the value of this kind of freedom can easily be explained – for example, free decisions lead to choosing the really best action (or more precisely: to choosing an action which with a high probability is not much worse than the really best action) – similar justifications of incompatibilist conceptions of freedom are missing. The concept of retrospective responsibility, on the other hand, is defined within a theory of social control of the course of the world, where ‘being responsible’, (very) roughly, means to be a good starting point for exerting such control. [A57; A93.]

            Moral psychology: In moral psychology I have developed a theory of the various motives for acting morally. A particular focus of the respective study [A50] is which of these motives are apt for defining a moral desirability function. – An outline of an ontogenetic psychology of moral judgements shows that in order for moral judgments to be stable in cases of acquiring new knowledge, they have to be founded on motives independent of moral considerations in the narrow sense, for example, on sympathy or respect. [A50: 20-24; A55.] – I have scrutinised the mechanisms and strength of sympathy in particular detail [B2: 589-616; A40].

            Theory of argumentation:
The epistemological approach to argumentation and the practical theory of argument:
I have developed an epistemological theory of argumentation, called “practical theory of argument”, which takes the production of knowledge or cognition (in the sense of justified belief) to be the standard function of argumentation. In other words, according to this approach, arguments are instruments for acquiring knowledge or cognition. This conception is in contrast to e.g. rhetorical or consensualistic approaches, which strive for changing the addressee’s belief or for consensus, irrespective of the truth of these beliefs. Other defenders of the epistemic approach include: John Biro, Richard Feldman, James Freeman, Alvin Goldman, Harvey Siegel, Mark Weinstein [cf. A70]. Some of the distinguishing features of my particular approach are:
•   a detailed analysis of the functional principle of rationally convincing by arguments (namely: guiding the addressee in a process of recognising the truth of the claim);
•   the separation of validity criteria for arguments, which define the features of a functioning instrument and whose observance implies the truth or high probability of the claim, from adequacy conditions, which are rules for the good usage of those instruments for rationally convincing;
•   the use of epistemological principles, taken from other philosophical disciplines, as the epistemic foundation for constructing epistemically valuable arguments and different argument schemes: in particular the principle of deductive implication, which is taken from logic; the principles of probability calculus; definitions of ‘(prudential) desirability’ or ‘utility’ taken from rational decision theory. [B1; A37; A68; A69.]
Various fields of argumentation theory: On the basis of this practical approach, I have developed several parts of a full-blown epistemological theory of argumentation: precise criteria for valid and adequate arguments in general [B1: 51-76; A68: sects. 6 and 8] and for several special types of arguments (deductive arguments [B1: 180-209], probabilistic arguments [A94], practical arguments for value judgements [B1: 319-433], genesis of knowledge arguments (arguments from authority, historiographic arguments, arguments from testimony …) [B1: 246-260], interpretive arguments [B1: 221-246; A17; A86], Pascal arguments (practical arguments for empirical claims) [A27], ethical arguments [A79; A83], practical justifications [A38.2]); a systematisation of argument types and schemes [A97]; a theory of fallacies [A42]; an approach to interpreting (ordinary language) arguments [A59; B1: 85-163]; a theory of truth-oriented argumentative dialogues [A1; A15].

            Metaphilosophy: My main contribution to metaphilosophy is a theory of philosophical theories, which reconstructs the types of currently existing clear and sensible theories in philosophy – “sensible” in that they provide reliable results of practical importance. The primary focus of this metaphilosophy is on the type of content of philosophical theories: which kinds of (systems of) hypotheses do philosophical theories try to establish? The methodological question is derivative: which methods can establish the desired kind of knowledge? I have found three types of philosophical theories: 1. descriptive-nomological theories (they try to provide empirical laws or regularities and explanations – as e.g. in cosmology or moral psychology or philosophical anthropology in general), 2. idealising-hermeneutic theories (they try to capture the practical sense of human constructs – e.g. in philosophy of language, logic, philosophy of science, ethics, theory of argumentation), and 3. technical-constructive theories (they try to improve already known instruments or to invent new useful ones – most of the idealising-hermeneutic theories have technical constructive counterparts, so e.g. logic, philosophy of science, ethics and theory of argumentation, etc.,  also have technical-constructive parts). [A96; B1: 10-21; A2.]
Constructive philosophy: I have developed philosophical theories of all three types – which is also visible e.g. in my three kinds of contributions to action philosophy. I especially like the constructive aspect of philosophy, particularly inherent in technical constructive theories. Even good philosophical and metaphilosophical epistemologies and methodologies have this constructive feature. And only the stringent and enlightening use of the epistemological principles and methods (re-)constructed by them leads to clear, reliable, systematic and valuable findings. The vignette at the top of this website is intended to express these aspects.

Current and future research projects

Apart from the many minor projects, my main research project at this time is to complete a wide-ranging theory of action and present it in a monograph.