However, Kelly had doubts about the practicality of humanistic psychology (Benjafield, 2008). Kelly's approach to psychology has some shared characteristics of humanistic psychology, but it also has its own peculiarities. Finally, Benjafield discussed the idea that Kelly could not be compared to either Maslow or Neisser. Although Maslow and Neisser had excellent educational backgrounds, Kelly had by far the most different. Kelly's previous studies in mathematics made him strongly influenced by Herbart. Herbart was by no means the most influential person in Kelly's life. Kelly mentioned people like Charles Darwin and Sigmund Freud in works like The Psychology of Personal Constructs (A Theory of Personality). However, Kelly was often vague when it came to referencing his sources, which presents many problems (Benjafield,