醫師能準確診斷出病人的問題，要靠熟練的臨床推理。近代文獻指出臨床推理是醫師在看病人時自然地以非分析性及分析性雙重思考交互運作的過程。醫師由病人的主訴做初步假設。根據假設以及病人的資訊，如可以辨認病人的症狀或症候，就會使用非分析性的思考過程。但如果醫師未能辨認出症狀症候，就會運用分析性推理思考，包含假設的測試、鑑別診斷、以及有條理地連接相關病程，來解釋臨床上的發現，進而釐清、闡明假設，得到診斷。醫師都是運用這兩種雙重運轉的推理思考模式，以「初步假設」推展一連串的推理思考過程來建立診斷。不論是非分析性或分析性或思考，都需要初步假設，才能有效地推演進一步的臨床思慮與鑑別診斷。

Physicians rely on proficient clinical reasoning to make accurate and timely diagnoses. Current literature suggests that clinical reasoning is based on the dual process theory, integrating non-analytical and analytical models of thinking and decision making process. In a clinical encounter, a physician generates initial hypotheses according to the patient’s chief complaint. Based on these hypotheses, a physician gathers further information by taking the patient’s history and performing physical examinations. The non-analytical thinking process is spontaneously triggered when a physician recognizes the patient’s clinical manifestation, which allows him/her to make a diagnosis. If the patient’s presentation is not familiar to the physician, the analytic process is activated, including verifying the hypotheses, refining differential diagnoses by correlating the working diagnosis and the disease progress as efforts for establishing the diagnosis. The non-analytical thinking process is comprised of intuitive, experiential and spontaneous pattern recognition. It uses information which is readily available, and therefore is rapid. The analytical thinking process involves a conscious, deliberate process guided by critical thinking based on additional available information. It engages analytical reasoning, and therefore, is thorough and slow. In practice, physicians apply both non-analytical and analytical model of reasoning throughout the diagnostic and decision-making process. In the dual process, preliminary hypotheses are vital to empower further clinical reasoning.