I thought, Behaviors define the "behavior" of objects, therefore: Integer is a behavior, because it defines the behavior of "integer objects" Integer class is a behavior because it defines the behavior of the object "Integer". 5 isBehavior -> false. Integer isBehavior -> true. Integer class isBehavior -> true. What about Traits? Traits are "behavioral(?)", but they don't define the behavior alone, only the composition of Traits in an actual class defines the behavior of an Object. TClass isBehavior -> false. So far so good. Smalltalk globals allBehaviors includes:TClass -> true ! No suprise, because #allBehaviors explicitly collect all classes and traits. But the question is, what do we want to call a "Behavior"? All Classes and MetaClasses (-> Behavior allSubclasses) All Classes and Traits All Classes and Traits and MetaClasses and ClassTraits All Classes and MetaClasses and some Traits? (this of course, is related to http://forum.world.st/RBEnvironments-allClasses-Traits-Meta-tp4796370.html). In squeak Traits are behavior too. nicolai