As elaborated in Heppner, Wampold, and Kivlighan(2008), Charles Peirce, a nineteenth-century American mathematician, philosopher, and logician, introducted four ways of knowing the truth:
1. The method of tenacity: Whatever belief one firmly adheres to is truth. These “truths” are known to be true because we have always known them to be true. Frequent repetition of these “truths” seems to enhance their validity.
2. The method of authority: If noted authorities such as the president of the United States, a state governor, a well-known psychologist, or a clinical supervisor say it is so, then it is the truth.
3. The a priori method (method of intuition): This method is based on the notion that what agrees with reason, what makes sense, is true.
4. The scientific method: It involves empirical tests to establish verifiable facts.
5. Bonus method: Learning through one’s own direct experiences in the world. Through countless experiences, each individual construes a “reality” of the world; some of his or her perceptions may match those of others with similar experiences, whereas other perceptions and conclusions about the world may not match those of others. Dangers exist if this method is used alone because biases can develop or information can be distorted. Moreover, the events we experience can represent a biased sample, which in turn can lead to inaccurate conclusions.
Heppner, P. P., Wampold, B. E., & Kivlighan, Jr., D. M. (2008). Research Design in Counseling (3rd ed.). Belmont, CA: Thomson Higher Education.