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In meta-ethics, the is-ought problem was articulated by David Hume (Scottish philosopher and historian, 1711–1776), who noted that many writers make claims about what ought to be on the basis of statements about what is. However, there seems to be a significant difference between descriptive statements (about what is) and prescriptive or normative statements (about what ought to be).

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

In every system of morality, which I have hitherto met with, I have always remark'd, 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 surpriz'd 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 shou'd be observ'd and explain'd; 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 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"? In other words, given knowledge of the way the world is, how can one know the way the world ought to be? 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]

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—the so-called naturalistic fallacy.


The apparent gap between "is" statements and "ought" statements, when combined with Hume's fork—the idea that all items of knowledge are either based on logic and definitions or on observation—renders "ought" statements of dubious validity. Since "ought" statements do not seem to be known in either of the two ways mentioned, it would seem that there can be no moral knowledge. Two responses to this are moral skepticism and non-cognitivism.

The answer of those who believe in actual moral knowledge depends upon a few presuppositions. One has to do with the definition of reality to which descriptive truths are said to correspond. Another has to do with the existence of indefinables.

An effective moral cognitivist response 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.

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)[4]

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. [5]

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 claims) 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.[6]

Criticisms and responsesEdit

A handful of arguments have been proposed which claim to show that an "ought" can actually be derived from an "is". John Searle devised one such argument.[7] It 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—would seem to depend upon general recognition of those institutions and their value.[8]

Many modern naturalistic philosophers see no impenetrable barrier in deriving "ought" from "is" believing an "ought" can derive from an "is" whenever we analyze goal-directed behavior, and a statement of the form "In order for A to achieve goal B, A ought to do C" exhibits no category error and may be factually verified or refuted.

Of course, it can be argued that this doesn't really address the problem, since the "goal" is an implied ought. The argument would amount to nothing more than deriving an ought from an ought. And conversely, it can be argued that the "means" is only an is and that the "goal" is a hypothetical is.

The moral philosopher Alasdair MacIntyre has attempted to show that because ethical language developed in the West in the context of a recognition of 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 the telos. In an evaluative capacity, therefore, "good" and "bad" carry moral weight without committing a category error. Just as a pair of scissors that cannot easily cut through paper can legitimately be called "bad" since it cannot discharge its function well, a doctor who cures a high percentage of his or her patients, or a person who acts in accordance with his or her particular culture's or community's vision of the human telos, can be called good, as can those things that help them facilitate their goal. It follows that if we want scissors to be good, we ought not make them like the aforementioned pair; if doctors or people in general want to be good, they ought to act in such ways, and make use of such things, that enable them to fulfill their telos.[9]

For some naturalists, simple ethical ought-beliefs such as "thou shalt not kill" follow naturally from human biological drives such as pair-bonding and avoiding unnecessary violence (although this ignores the reality of competing drives). The more complex ethical rules of society are derived for mutual benefit, and are perhaps amenable to an ethical methodology such as utilitarianism. The wider investigation of how social rules arise during group evolution belongs to the scientific field of sociobiology.

In contrast, those who propose supernaturalist origins of morality (maintaining is/ought incommensurability) assert these similarities between ethical rules and natural biological behavior are just coincidental. By itself supernaturalism fails to elucidate morality since the supernaturalist must additionally show how we are to choose between competing supernatural ethical systems without appealing to naturalistic principles such as minimizing suffering. Consequently naturalists claim a supernaturalist approach to ethics appears arbitrary and has no explanatory advantage.

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.

See also Edit

References Edit

  1. Hume, David (1739). A Treatise of Human Nature. London: John Noon. p. 469. Retrieved Oct 6, 2009. 
  2. Stephen Priest The British Empiricists, pp. 177-8, Routledge, 2007 ISBN 978-0415357234
  3. see Max Black, The Gap Between 'Is' and 'Should', The Philosophical Review, Vol. 73, No. 2. (Apr., 1964), pp. 165-181.
  4. see Aristotle's Nicomachean Ethics 6.2
  5. 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.
  6. See for example Ruggiero, Thinking Critically about Ethical Issues, 5th ed., Ch. 6.
  7. Searle, John R. "How to Derive 'Ought' From 'Is'", Philosophical Review 73, 1964, pp. 43-58.
  8. Searle, John R. (1995). The construction of social reality, New York: Free Press. ISBN 0029280451
  9. MacIntyre, Alasdair, After Virtue: A Study in Moral Philosophy (Notre Dame, IN: University of Notre Dame Press, 1981), 148-150.

Further reading Edit

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