122 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



physically. They are ways of thinking about events, though 

 they are presumably based upon the characters of the 

 events themselves, and there are right and wrong ways of 

 performing them. 



Classifying may be briefly described as the operation of 

 representing an event or its properties by a concept. The 

 concept may be chosen because of the general character 

 of the event as a whole, as when one describes a substance 

 as gold, or it may be chosen because of some obvious feature 

 of the event, as when one describes gold as yellow, lustrous, 

 and hard. Concepts are class-notions, having generality of 

 reference. A concept refers extensionally or denotatively 

 to the totality of events exemplifying or illustrating it. 

 This totality is called a class. Classes are determined 

 extensionally if one enumerates the members and then 

 searches for the concept which will describe all of them; 

 classes are determined intensionally if one starts with a 

 concept and then looks about for events exemplifying it. 

 When a given event is classified it is placed (mentally) 

 with other events exemplifying the same concept. When a 

 concept is available for use, classification is identification or 

 recognition; but when no concept in the language has pre- 

 cisely the required meaning, classification is the devising of 

 a new symbol which will prepare for future identification or 

 recognition. An event may lie in many classes if it has 

 many properties; gold, for example, lies in the class of 

 yellow things, of lustrous things, and of hard things. 



Ordering may be described as the operation of representing 

 a certain specific relational property of events by a concept. 

 Events may be ordered if (1) they may be classified, and 

 (2) there exists between every two members a relation 

 which is (a) asymmetrical and (6) transitive. This is the 

 technical definition of the notion. Property (1) states that 

 events which are capable of order must be like one another 

 in some respect, usually the respect according to which 

 they are to be ordered. For example, all hard objects 

 may be put into a class, or all lengths. Property (2) states 



