Is/Ought Distinction

The is/ought distinction, a foundational concept in moral philosophy, asserts that one cannot logically derive prescriptive moral or ethical conclusions (what ought to be) solely from descriptive factual premises (what is). This principle is often attributed to the Scottish philosopher David Hume, who observed in A Treatise of Human Nature (1739) that authors frequently transition from statements of fact to statements of obligation without providing a clear logical bridge. This logical gap is sometimes referred to as 'Hume's Guillotine' due to its perceived decisive separation of facts and values.

Origins and Philosophical Context

Hume's original observation was a critique of rationalist attempts to derive morality from reason or observation alone. He argued that moral judgments arise from sentiment or feeling, not from logical deduction. For example, observing that humans do engage in aggression does not logically entail that humans ought to be aggressive, nor does it mean that aggression ought to be condoned. Similarly, the fact that a behavior might be 'natural' or 'evolved' does not automatically render it 'good' or 'right'.

Later philosophers, including G.E. Moore in Principia Ethica (1903), further elaborated on this distinction through the concept of the 'naturalistic fallacy'. Moore argued that it is a fallacy to define moral terms like 'good' in terms of natural properties (e.g., pleasure, survival, evolution). To say that something is good because it is natural is to commit this fallacy, as it conflates a descriptive property with a prescriptive one. The naturalistic fallacy is a specific instance of violating the is/ought distinction.

Relevance to Evolutionary Psychology

In evolutionary psychology, the is/ought distinction serves as a critical methodological and conceptual boundary. Evolutionary explanations aim to describe the origins and mechanisms of human psychological traits and behaviors, including those related to morality, cooperation, aggression, and sexual behavior. They seek to understand why certain traits exist and how they functioned to promote fitness in ancestral environments. However, these descriptive accounts do not, by themselves, dictate how humans should behave in contemporary society, nor do they provide a foundation for moral judgments.

For instance, evolutionary psychologists might propose that certain sex differences in mating strategies (e.g., Buss, 1989) or parental investment (e.g., Trivers, 1972) evolved due to differing reproductive challenges faced by males and females. These are empirical claims about evolved predispositions. However, critics and proponents alike emphasize that such findings do not imply that these evolved predispositions ought to be maintained, encouraged, or considered morally superior or inferior in modern contexts. To argue that because men are (or were ancestrally) more prone to certain aggressive behaviors, they ought to be excused for such behaviors, or that society ought to structure itself to accommodate these behaviors, would be to commit the naturalistic fallacy and violate the is/ought distinction.

Similarly, the existence of evolved mechanisms for in-group favoritism or out-group prejudice (e.g., Kurzban & Leary, 2001) does not mean that such prejudices ought to be accepted as morally justifiable. Evolutionary accounts can help explain the roots of such phenomena, but they do not provide moral justification for them. Understanding the evolved basis of a behavior can inform strategies for managing or mitigating its negative consequences, but it does not prescribe whether it should be managed or mitigated.

Critiques and Nuances

While the is/ought distinction is widely accepted in philosophy and science, its absolute rigidity has been debated. Some philosophers, such as John Searle (1964), have argued that certain institutional facts can bridge the gap. For example, if one promises to do something, then one ought to do it. Here, the 'ought' seems to be derived from the 'is' of the promise-making institution. However, even in such cases, critics argue that the 'ought' ultimately rests on a prior, unstated moral premise about the obligation to keep promises.

In evolutionary psychology, the distinction is often invoked to counter charges of 'genetic determinism' or 'moral relativism.' By maintaining the distinction, researchers can pursue descriptive scientific inquiry into human nature without being seen as endorsing or justifying particular moral or social arrangements. Proponents like Tooby and Cosmides (1992) explicitly state that evolutionary psychology describes the architecture of the human mind as it is, not as it ought to be, and that scientific findings cannot dictate moral values. They argue that understanding evolved mechanisms can, in fact, empower individuals to choose behaviors that align with their chosen moral values, rather than being blindly driven by evolved predispositions.

Conversely, some critics of evolutionary psychology sometimes conflate descriptive evolutionary claims with prescriptive moral claims, leading to misinterpretations or mischaracterizations of the field's aims. For example, if an evolutionary explanation is offered for a sex difference, it is sometimes incorrectly assumed that the explanation is also a justification for maintaining that difference or for assigning different social roles based on it. The careful application of the is/ought distinction helps to clarify that evolutionary explanations are descriptive accounts of evolved mechanisms, not moral endorsements of their outcomes.

Conclusion

The is/ought distinction remains a fundamental principle for evolutionary psychology, demarcating the boundaries between scientific description and moral prescription. It underscores that understanding the evolutionary origins of human nature provides insights into what is, but it does not, by itself, determine what ought to be. This separation allows evolutionary psychology to contribute to a scientific understanding of human behavior without venturing into the realm of moral philosophy or policy advocacy.