As a special sentence type, generic sentences contribute a lot to the understanding of natural languages and have been a concern of semanticists, pragmatists and philosophers. In view of inefficiency of existing theoretical framework on generics, this paper addresses generics in the framework of cognitive linguistics. A type is a fictive entity, not an actual individual. It represents an abstraction from actuality which captures the commonality inherent across a set of actual instances. Conceptualization of generics is dynamic in nature. Generics’ syntax features and exceptions are both the natural result of cognitive processing, and truth conditions should be judged in terms of certain ICMs rather than the correspondence between linguistic expressions and reality of the physical world. It is concluded that fictivity, dynamicity and ICM (Idealized Cognitive Model) are three cognitive motivations, which are the answers to the puzzles of generics’ tolerating exceptions.