In chapter 14 of our psychology textbook, the chapter dealing with personality, we read about Freud's psychoanalytic theory of personality. As our book points out, "no aspect of Freud's theory is more controversial than his model of psychosexual development" (550). Freud claimed that ones sexuality began in infancy and that personality develops through a series of psychosexual stages. According to Freud, the success with which a person resolves each stage affects their personality. One interesting aspect of this is that if one does not successfully resolve a stage, fixation can occur.
There are certain habits and traits that Freud believed accompanied a persons fixation at a given stage. Here is an example of a person who exhibits the behaviors and/or traits Freud believed would accompany a person being fixated or "stuck" in a certain stage.
Ex. Brenda is twenty years old and still sucks her thumb. Although she is embarrassed about it, she won't quit because she gets immense comfort from it and often feels relaxed while doing it. She's also been known to bite her nails when bored and chew her pencils during an exam.
Can you guess which stage Freud would claim Brenda is fixated on? It is the oral stage.
Freud believed that becoming fixated in each stage would lead to a specific set of behaviors and/or traits. But looking at this one example and using the scientific thinking principals we can see why Freud may have been wrong. Freud is assuming a causation relationship between the behaviors Brenda exhibited and her experiences during what Freud deemed as the oral stage. We know that correlation does not equal causation and therefore unless Freud did systematic experiments to prove otherwise, he should not assume that Brenda becoming fixated in her oral stage has caused her to suck her thumb, bite her nails, and chew her pencils. Furthermore before assuming correlation-causation, Freud should do experiments to rule out rival hypothesis. It's plausible that all of Brenda's behaviors stem from a third variable.
So, while Freud's theory may be interesting it is important to remember that many have criticized it as pseudoscience and do not share Freud's view. As always keeping in mind the scientific thinking principals will allow one to analyze Freud's theory thoughtfully.