I'm confused about the precise terminology to use when referring to various subjects which are all related to making good choices. I know that axiology is general study of value, including moral, aesthetic, and potentially other types of value. Ethics is the strictly moral subfield of axiology. Within ethics, normative ethics focuses on what constitutes right and wrong behavior. It seems to me that normative ethics can be further subdivided, as it contains separate concerns about what we should morally value, and how to act given a set of moral values. I'll use the example of a utility-maximizing agent to illustrate this distinction, but only hesitantly, because I think it is also relevant to non-utilitarian agents.

The question "what is my utility function?" is obviously important to a utilitarian, who cares whether they will be maximizing aggregate felicity, preference satisfaction, or the share price of Facebook. Equally important, however, is the question "how should I act, in light of my utility function?" The difficulty of this problem may be less obvious, but thought experiments like Newcomb's problem show that two agents with the same answer to the first question can behave differently if they have different answers to the second.

I'd like to say that the second question is asking about normative decision theory, which studies optimal decision-making to maximize value, while taking no stance on what is actually valuable. But this creates a contradiction in my system of definitions: if normative decision theory doesn't concern actual value, then it can't be axiology. Yet normative decision theory still clearly recommends particular behaviors, so it is part of normative ethics. The problem is that ethics is supposedly a subfield of axiology, and we just decided that axiology excludes normative decision theory!

There are multiple resolutions to this contradiction: one could argue that

  1. axiology does in fact encompass normative decision theory,

  2. not all of normative ethics is axiology, or

  3. normative decision theory isn't normative ethics.

There might also be other ways to draw a coherent Venn diagram. I'd be curious to hear any justification for one of these fixes over the others.

2 Answers 2


According to reference here and here:

Normative decision theory is concerned with identification of optimal decisions where optimality is often determined by considering an ideal decision maker who is able to calculate with perfect accuracy and is in some sense fully rational.

Axiology is the philosophical study of value. It includes questions about the nature and classification of values and about what kinds of things have value.

Normative ethics is the study of ethical action. It is the branch of ethics that investigates the set of questions that arise when considering how one ought to act, morally speaking.

So normative decision theory is an interdisciplinary topic studied by economists, statisticians, data scientists, psychologists and philosophers, etc, thus it's an applied general topic which doesn't solely belong to either axiology or ethics branch of philosophy. And axiology intersects with normative ethics due to moral value as their common part, at least for moral realists. Actually many people confound ethics with axiology as reference here extensively talks about this confusion and the proposal for a new axiology.


Part of the problem here is that this question conflates two different senses of the term 'value':

  • The econometric sense, which uses 'value' as a noun to indicate (an often normalized) comparative worth
    • e.g., "Clean energy programs produce value that recovers all their initial research costs"
  • The philosophical sense, which uses 'value' as a noun or verb to indicate an attachment to an idealized state or goal
    • e.g., "We value sustainable and renewable energy for its preservation of the planet"

In fact, it's relatively easy to create quasi-paradoxical sentences with this term, such as "My values are not for sale, no matter what value you might offer in exchange." The econometric sense has been trying to worm its way into philosophy, particularly through rational actor theory and Libertarian ideologies, but it's an uncomfortable fit at best and an outright charade at its worst. Ideals are not generally subject to valuation.

Axiology is in fact the general philosophical term for the study of value, and ethics is one of its subfields. Normative decision theory is part of the rational actor model, and as such implicitly conflates the two forms of value. Normative decision theory can be used within an axiological framework, but it isn't axiological itself (except in the minds of certain economics-oriented philosophers). It's best to think of normative decision theory as a technology or methodology, not a philosophical position.

We should be a bit cautious with the distinction between conceptualization ("What do I value?") and implementation ("How should I act with respect to what I value?"), because they are not as separate as they might seem. For instance — and most of human history will bear me out on this — it's quite easy to say "I value peace and security as an ideal", then turn and say "They way I will achieve peace and security is by killing everyone who threatens me". One of the central problems of philosophical ethics is that conceptualizations and implementations must somehow be integrated and cohesive, or the ethical system collapses into bald-faced hypocrisy.

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