Editing Concept (section)

=== Classical theory ===
{{Main article|Definitionism}}

The classical theory of concepts, also referred to as the empiricist theory of concepts,<ref name="Origin of Concepts"/> is the oldest theory about the structure of concepts (it can be traced back to Aristotle<ref name="Big Book"/>), and was prominently held until the 1970s.<ref name="Big Book"/> The classical theory of concepts says that concepts have a definitional structure.<ref name="Stanford Encycl"/> Adequate definitions of the kind required by this theory usually take the form of a list of features. These features must have two important qualities to provide a comprehensive definition.<ref name="Big Book"/> Features entailed by the definition of a concept must be both ''[[necessity and sufficiency|necessary]]'' and jointly ''[[necessity and sufficiency|sufficient]]'' for membership in the class of things covered by a particular concept.<ref name="Big Book" /> A feature is considered necessary if every member of the denoted class has that feature. A set of features is considered sufficient if having all the parts required by the definition entails membership in the class.<ref name="Big Book" /> For example, the classic example ''[[bachelor]]'' is said to be defined by ''unmarried'' and ''[[man]]''.<ref name="Stanford Encycl"/> An entity is a bachelor (by this definition) if and only if it is both unmarried and a man. To check whether something is a member of the class, you compare its qualities to the features in the definition.<ref name="Origin of Concepts"/> Another key part of this theory is that it obeys the ''[[law of the excluded middle]]'', which means that there are no partial members of a class, you are either in or out.<ref name="Big Book"/>

The classical theory persisted for so long unquestioned because it seemed intuitively correct and has great explanatory power. It can explain how concepts would be acquired, how we use them to categorize and how we use the structure of a concept to determine its referent class.<ref name="Stanford Encycl"/> In fact, for many years it was one of the major activities in [[philosophy]]—[[formal concept analysis|concept analysis]].<ref name="Stanford Encycl"/> Concept analysis is the act of trying to articulate the necessary and sufficient conditions for the membership in the referent class of a concept.{{citation needed|date=December 2012}} For example, Shoemaker's classic "[[Time Without Change]]" explored whether the concept of the flow of time can include flows where no changes take place, though change is usually taken as a definition of time.{{citation needed|date=August 2020}}

==== Arguments against the classical theory ====
Given that most later theories of concepts were born out of the rejection of some or all of the classical theory,<ref name="concepts core readings"/> it seems appropriate to give an account of what might be wrong with this theory. In the 20th century, philosophers such as Wittgenstein and Rosch argued against the classical theory. There are six primary arguments<ref name="concepts core readings"/> summarized as follows:
* It seems that there simply are no definitions—especially those based in sensory primitive concepts.<ref name="concepts core readings"/>
* It seems as though there can be cases where our ignorance or error about a class means that we either don't know the definition of a concept, or have incorrect notions about what a definition of a particular concept might entail.<ref name="concepts core readings"/>
* [[Willard Van Orman Quine|Quine]]'s argument against analyticity in [[Two Dogmas of Empiricism]] also holds as an argument against definitions.<ref name="concepts core readings"/>
* Some concepts have fuzzy membership. There are items for which it is vague whether or not they fall into (or out of) a particular referent class. This is not possible in the classical theory as everything has equal and full membership.<ref name="concepts core readings"/>
* Experiments and research showed that assumptions of well defined concepts and categories might not be correct. Researcher Hampton<ref>{{cite journal |last1=Hampton |first1=J.A. |title=Polymorphous concepts in semantic memory. |journal=Journal of Verbal Learning and Verbal Behavior |date=1979 |volume=18 |issue=4 |pages=441–461|doi=10.1016/S0022-5371(79)90246-9 }}</ref> asked participants to differentiate whether items were in different categories. Hampton did not conclude that items were either clear and absolute members or non-members. Instead, Hampton found that some items were barely considered category members and others that were barely non-members. For example, participants considered sinks as barely members of kitchen utensil category, while sponges were considered barely non-members, with much disagreement among participants of the study. If concepts and categories were very well defined, such cases should be rare. Since then, many researches have discovered borderline members that are not clearly in or out of a category of concept.
* [[Eleanor Rosch|Rosch]] found typicality effects which cannot be explained by the classical theory of concepts, these sparked the prototype theory.<ref name="concepts core readings"/> See below.
* Psychological experiments show no evidence for our using concepts as strict definitions.<ref name="concepts core readings"/>