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David Hume raised the is-ought problem in his Treatise of Human Nature

The is-ought problem in meta-ethics as articulated by Scottish philosopher and historian, David Hume (1711–1776), is that many writers make claims about what ought to be on the basis of statements about what is. However, Hume found that there seems to be a significant difference between descriptive statements (about what is) and prescriptive or normative statements (about what ought to be), and it is not obvious how we can get from making descriptive statements to prescriptive. The is-ought problem is also known as Hume's Law and Hume's Guillotine.

A similar though distinct view is defended by G. E. Moore's open question argument, intended to refute any identification of moral properties with natural properties. This so-called naturalistic fallacy is contrasted by the views of ethical naturalists.


Hume discusses the problem in book III, part I, section I of his work, A Treatise of Human Nature (1739):

In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, 'tis necessary that it should be observed and explained; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.[1]

Hume asks, given knowledge of the way the universe is, in what sense can we say it ought to be different?

Hume calls for caution against such inferences in the absence of any explanation of how the ought-statements follow from the is-statements. But how exactly can an "ought" be derived from an "is"? The question, prompted by Hume's small paragraph, has become one of the central questions of ethical theory, and Hume is usually assigned the position that such a derivation is impossible.[2] This complete severing of "is" from "ought" has been given the graphic designation of Hume's Guillotine.[3]


The apparent gap between "is" statements and "ought" statements, when combined with Hume's fork, renders "ought" statements of dubious validity. Hume's fork is the idea that all items of knowledge are either based on logic and definitions, or else on observation. If the is-ought problem holds, then "ought" statements do not seem to be known in either of these two ways, and it would seem that there can be no moral knowledge. Moral skepticism and non-cognitivism work with such conclusions.

The is-ought problem has been recognised as an important issue for the validity of secular ethics and their defense from criticism - often religiously inspired.[4]


Oughts and goals[]

File:Alonzo Babers finish.JPEG

Few debate that one ought to run quickly if their goal is to win a race. A tougher question may be whether one "morally ought" to want to win a race in the first place.

Ethical naturalists contend that moral truths exist, and that their truth value relates to facts about physical reality. Many modern naturalistic philosophers see no impenetrable barrier in deriving "ought" from "is", believing it can be done whenever we analyze goal-directed behavior. They suggest that a statement of the form "In order for agent A to achieve goal B, A reasonably ought to do C" exhibits no category error and may be factually verified or refuted. "Ought"s exist, then, in light of the existence of goals.

This is similar to work done by moral philosopher Alasdair MacIntyre, who attempts to show that because ethical language developed in the West in the context of a belief in a human telos—an end or goal—our inherited moral language, including terms such as "good" and "bad," have functioned, and function, to evaluate the way in which certain behaviors facilitate the achievement of that telos. In an evaluative capacity, therefore, "good" and "bad" carry moral weight without committing a category error. For instance, a pair of scissors that cannot easily cut through paper can legitimately be called "bad" since it cannot fulfill its purpose effectively. Likewise, if a person is understood as having a particular purpose, then behaviour can be evaluated as good or bad in reference to that purpose. In plainer words, a person is acting "good" when they fulfill their purpose.[5]

Even if the concept of an "ought" is meaningful, this need not involve morality. This is because some goals may be morally neutral, or (if it exists) against what is moral. A poisoner might realize their victim has not died and say, for example, "I ought to have used more poison," since his goal is to murder. The next challenge of a moral realist is thus to explain what is meant by a "moral ought".[6]

Discourse ethics[]

Main article: Discourse ethics

Proponents of discourse ethics argue that the very act of discourse implies certain "oughts", that is, certain presuppositions that are necessarily accepted by the participants in discourse, and can be used to further derive prescriptive statements. They therefore argue that it is incoherent to argumentatively advance an ethical position on the basis of the is–ought problem, which contradicts these implied assumptions.

"Moral" oughts[]

As MacIntyre explained, someone may be called a "good person" if people have an inherent purpose. Many ethical systems appeal to such a purpose. This is true of some forms of Moral realism, which states that something can be wrong, even if every thinking person believes otherwise (the idea of brute fact about morality). The ethical realist might suggest that humans were created for a purpose (e.g. to serve God), especially if they are an ethical non-naturalist. If the ethical realist is instead an Ethical naturalist, they may start with the fact that humans have evolved and pursue some sort of evolutionary ethics (which risks 'committing' the moralistic fallacy). Not all moral systems appeal to a human telos or purpose. This is because it is not obvious that people even have any sort of natural purpose, or what that purpose would be. Although many scientists do recognize teleonomy (a tendency in nature), few philosophers appeal to it (this time, to avoid the Moralistic fallacy).

File:The Posts - - 116024.jpg

The greater challenge of ethical systems is often defining the nature and origins of the "good" that one ought to pursue

Goal-dependent oughts run into problems even without an appeal to an innate human purpose. Consider cases where one has no desire to be "good" - whatever it is. If, for instance, a person wants to be good, and 'good' means washing one's hands, then it seems one morally ought to wash their hands. The bigger problem in moral philosophy is what happens if someone does not want to be 'good', whatever its origins? Put simply, in what sense ought we to hold the goal of being good? It seems one can ask "how am I rationally required to hold 'good' as a value, or to pursue it?"[7]

The issue above mentioned is a result of an important ethical relativist critique. Even if "oughts" depend on goals, any moral ought would vary with the person's goal. This is the conclusion of the ethical subjectivist, who says a person can only be called "good" according to whether they fulfill their own, self-assigned goal. Alasdair MacIntyre himself suggests that a person's purpose comes from their culture, making him a sort of Ethical relativist.[8] Ethical relativists acknowledge local, institutional facts about what is right, but these are facts that can still vary by society. Thus, without an objective "moral goal", a moral ought is difficult to establish. If moral goals depend on private assumptions or public agreement, so may morality as a whole. For example, Canada might call it "good" to maximize global welfare, where a citizen, Alice, calls it "good" to focus on herself, and then her family, and finally her friends (with little empathy for strangers). It does not seem that Alice can be objectively or rationally bound - without regard to her personal values nor those of groups of other people - to act a certain way. In other words, we may not be able to say "You just should do this". Moreover, persuading her to help strangers would necessarily mean appealing to values she already possesses (or else we would never even have a hope of persuading her).[9]

There may be some possible responses to this relativistic critique. As mentioned above, Ethical realists that are non-natural can appeal to God's purpose for man. On the other hand, naturalistic thinkers may posit that valuing people's well-being is somehow 'obviously' the purpose of ethics, or else the only relevant purpose. This is the move made by Natural law, Scientific moralists and some utilitarians.

Institutional facts[]

John Searle also attempts to derive "ought" from "is".[10] He tries to show that the act of making a promise places one under an obligation by definition, and that such an obligation amounts to an "ought". This view is still widely debated, and to answer criticisms, Searle has further developed the concept of institutional facts, for example, that a certain building is in fact a bank and that certain paper is in fact money, which would seem to depend upon general recognition of those institutions and their value.[11]


Indefinables are concepts so global that they cannot be defined; rather, in a sense, they themselves, and the objects to which they refer, define our reality and our ideas. Their meanings cannot be stated in a true definition, but their meanings can be referred to instead by being placed with their incomplete definitions in self-evident statements, the truth of which can be tested by whether or not it is impossible to think the opposite without a contradiction. Thus, the truth of indefinable concepts and propositions using them is entirely a matter of logic.

An example of the above is that of the concepts "finite parts" and "wholes"; they cannot be defined without reference to each other and thus with some amount of circularity, but we can make the self-evident statement that "the whole is greater than any of its parts", and thus establish a meaning particular to the two concepts.

These two notions being granted, it can be said that statements of "ought" are measured by their prescriptive truth, just as statements of "is" are measured by their descriptive truth; and the descriptive truth of an "is" judgment is defined by its correspondence to reality (actual or in the mind), while the prescriptive truth of an "ought" judgment is defined according to a more limited scope—its correspondence to right desire (conceivable in the mind and able to be found in the rational appetite, but not in the more "actual" reality of things independent of the mind or rational appetite)[12]

To some, this may immediately suggest the question: "How can we know what is a right desire if it is already admitted that it is not based on the more actual reality of things independent of the mind?" The beginning of the answer is found when we consider that the concepts "good", "bad", "right" and "wrong" are indefinables. Thus, right desire cannot be defined properly, but a way to refer to its meaning may be found through a self-evident prescriptive truth.[13]

That self-evident truth which the moral cognitivist claims to exist upon which all other prescriptive truths are ultimately based is: One ought to desire what is really good for one and nothing else. The terms "real good" and "right desire" cannot be defined apart from each other, and thus their definitions would contain some degree of circularity, but the stated self-evident truth indicates a meaning particular to the ideas sought to be understood, and it is (the moral cognitivist might claim) impossible to think the opposite without a contradiction. Thus combined with other descriptive truths of what is good (goods in particular considered in terms of whether they suit a particular end and the limits to the possession of such particular goods being compatible with the general end of the possession of the total of all real goods throughout a whole life), a valid body of knowledge of right desire is generated.[14]

Other responses[]

The broad term moral cognitivist is the meta-ethical view that ethical sentences express propositions and can therefore be true or false (they are truth-apt).

One response of those who believe in actual moral knowledge depends upon a few presuppositions. One type of moral cognitivist, the moral realist, asserts that the term "reality" designates (or connotes) those things actually existing independent of the mind, rather than those representations of such things in the mind that we call knowledge, or of wishes entertained that things might be otherwise. An effective moral cognitivist response maintains that the truth of "is" statements is ultimately based on their correspondence to reality (both in the realm of actuality and the ideal), while that of "ought" statements is not.[citation needed]

American philosopher David Alan Johnson attempted to refute the notion of an is-ought gap in his work "Truth Without Paradox" in which he presents three lines of reasoning challenging the idea of a deductive gap between normative and factual propositions.

The Dutch scholar Hendrik Gommer published in 2010 the article 'From the 'is' to the 'ought': a biological theory of law' in which he states that the 'is-ought' problem should be solved in order to make a necessary next step towards thinking about the biological foundations of law.[15] Biology can for example explain why people sometimes value killing another human being as 'good' (i.e. 'ought') and sometimes as 'bad' (i.e. 'ought not'). Killing the enemy is good because it saves our children, killing my neighbour is bad because it destabilises society. Morals and rules have evolved from biological facts and are the result of interaction between genes and their surroundings. They are a product of our brain as all interpretations of facts are. As a result, 'goodness' can be regarded as a biological phenomenon.

[G. E. M. Anscombe] offers a response in her highly influential paper "Modern Moral Philosophy."

See also[]


  1. Hume, David (1739). A Treatise of Human Nature, London: John Noon. URL accessed Oct 6, 2009.
  2. Stephen Priest The British Empiricists, pp. 177-8, Routledge, 2007 ISBN 978-0-415-35723-4
  3. see Max Black, The Gap Between 'Is' and 'Should', The Philosophical Review, Vol. 73, No. 2. (Apr., 1964), pp. 165-181.
  4. Craig, Robin. Good Without God. pp 349-361 in Bonett, Warren (Editor). 2010.The Australian Book of Atheism. Melbourne, Vic: Scribe ISBN 9781921640766 [1]
  5. MacIntyre, Alasdair,After Virtue: A Study in Moral Philosophy(Notre Dame, IN: University of Notre Dame Press, 1981), 148-150.
  6. H. L. A. Hart's The Concept of Law (1994)
  7. These ideas are discussed extensively in Richard Joyce's The Myth of Morality (2001)
  8. discussed in J. L. Mackie's Ethics: Inventing Right and Wrong(1997)
  10. Searle, John R. "How to Derive 'Ought' From 'Is'",Philosophical Review 73, 1964, pp. 43-58.
  11. Searle, John R. (1995). The construction of social reality, New York: Free Press.ISBN 0-02-928045-1
  12. see Aristotle's Nicomachean Ethics 6.2
  13. As an example of philosophical argumentation that identifies particular indefinables, we take "being" and then "good". Aristotle stated that although being is not a genus (Posterior Analytics 2.7), yet of everything that is, being is predicated (Topics 4.1), and that the Genus-differentia definitions, of which he was the first recorded proponent, requires that its subject be defined through its genus and a differentia. But since nothing lies outside of what is predicated of being, there is nothing which can serve as a differentia. So being is postulated to be indefinable. Later, Aquinas made an argument that stated, "Good and being are the really the same, and differ only according to reason.... [G]ood presents the aspect of desirableness, which being does not present." (Summa Theologica, Part I, Q. 5, Art. 1) So good is postulated to be indefinable.
  14. See for example Ruggiero, Thinking Critically about Ethical Issues, 5th ed., Ch. 6.
  15. Hendrik Gommer, From the 'is' to the 'ought', Archiv für Rechts- und Sozialphilosophie 2010, p. 449-468; also A Biological Theory of Law. Natural Law Theory Revisited, Amazon 2011.

Further reading[]

  • Template:Sep
  • Gerhard Schurz, The is-ought problem. An investigation in philosophical logic Dordrecht, Kluwer, 1997.


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