What is the difference between class and concept? − I am not sure whether, for instance, “chair” is typically a class or rather a concept, or both. I would say that it is only a class, though it is usual to say that it is a concept.
Some further reflections, in answer to the comments below, in order to expound the question:
If one reads the interesting comments by Mauro ALLEGRANZA below, one would think: So, the concept is the intension, and the class is the extension?
It has been hinted in the source, mentioned in my answer to virmaior (in the comments below) that the difference between “class” and “concept” were the following (I explain it a bit more extended than in the source, as I understand it, adding examples, but without really changing it in essence):
- concept: − The fact that certain properties have been empirically found, is the motivation to define a new concept (comprising objects with those properties). E.g. the concept "wood" for ubiquitously growing plants that are a suitable material to produce spears and arches. – This new concept has been created as intensional predicate. In this sense Aristotle used it in his syllogisms. This might be called logic of concepts.
- class: − A certain empirically found, additional property is attributed to an existing concept, e.g. the property "combustible" to the concept "wood". Hence, all woods are now members of the new class “combustible object”. – This new class has been created as a extensional predicate. In this sense class is used in Venn diagrams, and G. Boole used it about in this sense, too. This may be called logic of classes.
But now, the really big question follows, to wit, whether a class like “combustible objects” is a concept, or not. And whether a concept like “wood” is a class. This is the real reason for my question, because this has never been discussed, as far as I know.
In the case of “chair”, I imagine that, while everybody was sitting on the floor, some king once said that he wants to sit down conveniently and someone designed something like a singleton of a chair. Subsequently, all objects that were similarly agreeable to sit, were also called chair.
Is chair now a class or a concept? An how is it for more abstract “things” as for instance “discernment” or “equality” (in the Masonic/communist/French Revolution sense)?
If it were true that concepts are different from classes, in the sense that concepts do not have assigned parallel classes, and vice versa; this would not merely be a theoretical issue, since it would imply that philosophy and science should increase its focus more on concepts, and less on classes.
A further question would also be, whether there exist special (intrinsically “aristocratic”) classes, which have been automatically upgraded to concepts and vice versa.