The incompleteness triggers an internal search, and the imagination generates possible referents to complete its meaning and establish closure. Although most of us are unaware of this mental operation, we do it continually as we try to make sense of what we're being told. A word whose meaning is incomplete is a class . The various meanings that can be assigned to that word are members of the class. Lassie is a member of the class dog because Lassie can complete the meaning of dog .
Some classes have other classes as members.
The class animal has the class dog as a member because dog can complete the meaning of animal . If I ask you to imagine a dog, you probably won't think of Morris the Cat. But if I ask you to imagine an animal, you might think of Lassie or Morris since both dogs and cats are animals. The more inclusive the class, the greater the number of meanings one can assign to it. The late psychiatrist Milton H. Erickson, an innovative practitioner of clinical hypnosis, recognized this fact and incorporated such ambiguities into his trance inductions.