Abstract
Basic knowledge and information are acquired through the language in the family, society and education, which should be based on philosophy and logical principles. In the field of medicine, a dialog can be established between the doctor and the patient for diagnosis with linguistic (verbal, oral) information exchange rather than mathematical expressions. This chapter presents rational thinking with logical principles, preferably combining the basic principles of philosophy in medicine with the treatment of uncertainty, the results of which are presented according to the usual bivalent (crisp, two-value) logic. The necessary and effective structural steps of rational use of language are presented based on verbal knowledge and uncertainties in information production. It is emphasized that innovative ideas, procedures and methods are possible through research and development activities, if the language, philosophy, and logic principles are observed for the most reasonable cases, even with approximate decisions.