One approach to the meaning of language emphasizes the idea that meaning is conventional. Thus, when we interpret a constitutional or statutory provision, we might like for the conventional semantic meaning of the word or phrase. But there is another view in the philosophy of language that rejects the idea that all meaning is conventional. This approach has its greatest intuitive appeal in the case of words like "gold" or "water" that refer to natural kinds. Thus gold is the name of an element with an atomic structure, and water is the name for a substance defined by a molecular structure (H20).
The idea of natural kinds that have an essential structure could be extended to what might be called "moral kinds" or "functional kinds." Thus it could be argued that legal concepts like "cruelty," "guilt," "reasonableness," or "causation" are not defined conventionally, but instead have an essence that defines their true nature.
This entry in the Legal Theory Lexicon provides a very short introduction to the idea of natural and moral kinds. As always, the Lexicon is aimed at law students with an interest in legal theory.
A conventional approach to language might lead to the conclusion that a word like "gold" or "water" has whatever meaning is revealed by the patterns of usage that establish its conventional meaning, but there is a powerful argument that this is not the case. Gold and water are natural kinds, the nature of which can be determined by scientific investigation. Whether something really is gold or water doesn't depend on the way we talk, it depends on physics and chemistry. A famous example is "jade," which was once thought to be a single substance. When modern science revealed that what we had been calling "jade" was actually two different substances ("jade" and "jadeite"), we learned that we had been making a mistake when we called jadeite "jade."
The idea of natural kinds was developed by philosophers. The key figures are Saul Kripke and Hilary Putnam. Some of their writings are cited in the bibliography below.
Natural kind terms play a role in the law, but that role is limited. For example, the United States Constitution refers to gold and silver in Article One. If these substances are natural kinds, then their meaning in the constitutional text might be determined by the best scientific theory of their nature. But the law frequently uses terms that do not refer to natural kinds that are investigated by science. Examples might include "unreasonable" in the Fourth Amendment, "cruel" in the Eighth Amendment, or "freedom of speech" in the First Amendment.
Moral and Functional Kinds
The existence of natural kinds with essences that are revealed by natural science is relatively uncontroversial. More controversial is the idea that there might be moral or functional kinds. If this idea is correct that it would have important implications for the interpretation of legal texts. When judges were trying to determine what is "unreasonable" they would investigate the nature of reasonableness; the best theory of what is reasonable would then guide the determination of what searches are "unreasonable" for Fourth Amendment purposes. Likewise, judges interpreting the First Amendment would try to determine the true nature of "freedom of speech" and then apply that theory to determine what constitutes a violation of the First Amendment.
This idea has been most extensively developed by the great legal philosopher Michael Moore; his most important article on the notion of functional kinds and its role in legal interpretation is cited in the bibliography that appears below. Moore's idea is very different that the use of the concept-conception distinction by Ronald Dworkin: that notion is explored in a separate Legal Theory Lexicon entry.
The notion of natural kinds and the related ideas of moral and functional kinds pose an important challenge to conventionalist accounts of legal interpretation. This is a deep topic, but my hope is that this Lexicon entry provides a basic introduction that is accessible to students without background in philosophy.
Related Lexicon Entries
- Alexander Bird & Emma Tobin, "Natural Kinds", The Stanford Encyclopedia of Philosophy (Spring 2017 Edition), Edward N. Zalta (ed.), URL = <https://plato.stanford.edu/archives/spr2017/entries/natural-kinds/>.
- Saul Kripke, Naming and Necessity (1980).
- Michael Moore, The Semantics of Judging, 54 S. Cal. L. Rev. 151 (1980-1981).
(First version, May 7, 2017)