In the second lecture note, possibilistic models and fuzzy system models based on the logics are explained.There are several modalities in system models where human estimation is influential. Thus, it is necessary to construct system models based on concepts of the possibility and the necessity. In applications, fuzzy mathematical programming, possibilistic linear regression analysis and the decision problem by the evidence theory are described, and the fuzzy inference related to fuzzy logical systems is illustrated. The fuzzy inference has been already used in fuzzy control systems and will be promising in expert systems.