Abstract
The main information in this chapter is about logic, which helps to reach more rational and productive thoughts and ideas about an event involving medical sciences. In general, after the philosophical thinking principles, the logical rules lead to inferences that are more rational, and therefore, knowledge becomes more applicable. Logical words and propositions are explained on bivalent (crisp) and fuzzy logical rule-based expressions. Logic plays a very crucial role in the medical sciences, based on sound reasoning. Mathematics based on binary logical principles is useful in science, but fuzzy logic principles and rules play a central role with extreme predominance in medical science because communication between doctor and patient takes place linguistically before laboratory analysis for some numerical data.