Natural kind in the context of "Social construct"

A class is a collection whose members either fall under a predicate or are classified by a rule. Hence, while a set can be extensionally defined only by its elements, a class has also an intensional dimension that unites its members. When the term 'class' is applied so that it includes those sets whose elements are intended to be collected without a common predicate or rule, the distinction can be indicated by calling such sets "improper class."

Philosophers sometimes distinguish classes from types and kinds. The class of human beings is discussed, as well as the type (or natural kind), human being, or humanity. While both are typically treated as abstract objects and not different categories of being, types not classes are usually treated as universals. Whether natural kinds ought to be considered universals is vexed; see natural kind.

A causal theory of reference or historical chain theory of reference is a theory of how terms acquire specific referents based on evidence. Such theories have been used to describe many referring terms, particularly logical terms, proper names, and natural kind terms. In the case of names, for example, a causal theory of reference typically involves the following claims:

• a name's referent is fixed by an original act of naming (also called a "dubbing" or, by Saul Kripke, an "initial baptism"), whereupon the name becomes a rigid designator of that object.
• later uses of the name succeed in referring to the referent by being linked to that original act via a causal chain.

Weaker versions of the position (perhaps not properly called "causal theories") claim merely that, in many cases, events in the causal history of a speaker's use of the term, including when the term was first acquired, must be considered to correctly assign references to the speaker's words.