Abstract

In this article, Peirce’s conception of natural class is discussed. It is shown that Peirce’s mature conception of natural class is intimately related to his conception of causation. Peirce’s originality in respect of natural classes concerns at least two insights: first, he made clear that all classification, be it natural or artificial, must be related to some purpose. Secondly, natural classifications do not primarily involve our purposes, but the final causes of the classified things themselves. According to Peirce, things belong to the same natural class on account of a metaphysical essence and a number of class characters. The metaphysical essence is a general principle by virtue of which the members of the class have a tendency to behave in a specific way; this is what Peirce meant by final cause. This finality may be expressed in some sort of microstructure. The class characters, which by themselves are neither necessary nor sufficient conditions for membership of a class, are nevertheless concomitant. Natural classes, though very real, do not exist; their reality is of the nature of possibility, not of actuality. The primary instances of natural classes are the objects of scientific taxonomy, such as elementary particles in physics, gold in chemistry, and species in biology, but also man-made objects and social classes.