Carl Jung was one of the most famous psychiatrists next to Sigmund Freud. He introduced into our language such concepts as synchronicity, the collective unconscious and the archetype. He was a man who delved into mythology and folklore while still probing the human mind for its secrets. Despite his many accomplishments, there are some weaknesses and criticisms of his theories. His ideas were revolutionary, but they were also beyond belief at times.
Jung believed that people who had auditory hallucinations were hearing the words of the collective unconscious speaking directly to them. He did not consider these to be pathological. He actually considered them to be beneficial to the subject and necessary for self-improvement. This has been widely criticised and looked at as one of the weaknesses in Jung's theories. Instead of treating the hallucination, he would treat them as some benefit to the person.
Jung had a very confusing way of writing at times which leaves many of his theories up for debate. Some of the terminology he uses is vague and tough to understand. This makes it hard to fully appreciate what his theories mean because some terms can be used with multiple meanings. He also uses very obscure references that make his writings difficult for all but the most dedicated of students to get through.
Jung was not concerned with scientific testing, and many of his theories are not ones that can be tested in a laboratory setting. He was not concerned with things that could be measured, and this is a weakness in his theory. Jung's ideas cannot be tested to see if they are true because there is no way to test things like chance, collective unconscious and archetypes in the real world. His ideas are mystical and stray very far from scientific thinking.
Jung tried with his theories to include religion in psychology, and this is seen as a primary weakness in his theories. His studies in mysticism, folklore and mythology coupled with an abiding interest in religion led him to attempt to explain religion in psychological terms. Many psychologists do not feel that these issues can be explained by psychology. However, there are some that feel that Jung was revolutionary for trying to extend the practice into this area.