Abstract
There is an intense relationship between knowledge of the second and third kind in Spinoza’s classification of knowledge. Both of them are adequate, but only the second is the origin of the adequacy. Knowledge of the second kind consists of common notions, but common notions only constitute the essence of human body and what simpler than it. On the other hand, knowledge of the third kind is knowledge of essence of things. Therefore, the relationship between them and how knowledge of the second kind moves to the third become a problem. In this dissertation, I shall firstly evaluate two opposite interpretation and their flaws. And I will re-examine the definition of knowledge of the last two kinds, especially what are common notions and essence of things: the different degrees of common notions, and their difference with universal notions, what are singular things, how these things are defined, and finally what does essence mean. After these reevaluation, I will give my interpretation about how Spinoza, by changing the way definitions are formed, bridge the gap between knowledge of the last two kinds.