The present dissertation has as its theme a study of human nature, cognitive life and affective life in the way they were demonstrated by Spinoza in the second and third parts of his masterpiece, the Ethics. In order to achieve this goal we chose to carry out a thorough reading of this work, following his investigation of ideas as demonstrated by Spinoza himself and in the order they were presented by him. One of the great innovations of Ethics is its model of human nature that can not be separated from the divine nature as well as the impact that it represents for the process of formation of the singular modes in his philosophy. In the first part of this dissertation, we present the deductive process through which Spinoza establishes the human mind as something that must follow from thought and extension attributes, whose nature is responsible for the origin of singular modes, among them the human mode of existence. In the second part, we demonstrate how the doctrine of the unique substance is decisive for Spinoza s innovative conception of the mind-body union as well as the immediate effects it produces at the spinozist method s genders of knowledge. In the third and last part, we present an investigation on Spinoza s science of affects, closely examining each step of its demonstration within the Part III of the Ethics. After the presentation of these three stages of development of Spinoza s philosophy we intend to show that the author s demonstrations points that human nature is the result of a reality that unites cognitive life and affective life.