theory extended from W.I. Thomas' definition of the situation
("If men define situations as real, they are real in their consequences.")
Although many use this term in several generalized instances, the sociological definition actually states that a "self-fulfilling prophecy occurs when a false definiton of a situation evokes a new behavior that makes the originally false conception come true." (Judson R. Landis, 2001.)
An example of this was illustrated by psychologist Robert Rosenthal, who performed an experiment in which a teacher was told that a certain group of her students were incredibly smart. In fact, these children had average IQ and average performance in earlier grades, and they were no smarter than the rest of the children in the class. Rosenthal tested all the children later in the year and asked the teacher to give evaluations. In both tests AND recommendations, these students showed that they had made greater progress, were more interested, and had made greater leaps in intelligence.
Another example, a la Rosenthal: twelve students were given 5 rats each. 6 of the students were told that their rats were genetically superior and would be extremely talented at getting through a maze. The other 6 students were told that their rats were lazy, stupid, and inferior. Of course, there was no difference in intellect or capacity for learning between any of the rats; they had all been picked at random. The result? Even at the very beginning of the training process, the "smart" rats performed better. By the end of the training, there was a marked difference between the abilities and personalities of the rats in each group.
The explanation that sociologists have created for this theory is that once a label is placed on someone, people tend to believe that this label is true and will respond to a labeled individual as if the label were true. The individual, upon subconsciously recognizing the changes in behavior of the others towards him or herself, will adjust her behavior accordingly, and the label will actually BECOME true.
My own hypothetical example. Suppose that my boyfriend and I get in a horrible fight and he calls me a slut and tells me there is nothing good about my except my willingness to reveal my body. I am very hurt and depressed and, after noting his actions of rejection, start wearing revealing tank tops and short-shorts in desperation. Other people, then notice my change in behavior and begin to think of me as a slut (Let's hope this never happens.)
Hypothetical example 2. An average student is told by his parents that he is horrible at math. He considers his recent test scores and notes that although there are good grades, there are a couple failures among them. Every failure that he gets counts against him. Eventually, this student gives up trying in a subject that he is so decidedly horrible at. His A and B grades change to Fs... he is now ACTUALLY bad at math.