Among Plato's first dialogues, the Protagoras stands out as the work in which the so called ethical intellectualism is exposed in the most systematic manner. Roughly, in ethical intellectualism, ethical themes such as virtues or moral excellences (justice, piety, wisdom, temperance and courage) are defined exclusively as the result of a cognitive process; in other terms, for ethical matters to be correctly understood, a certain knowledge must be considered; in this case, knowledge of the good. This point is made clear at the end of the Protagoras: all virtues discussed throughout the dialogue are strictly one thing, namely knowledge. The consequences of the intellectualist ethical doctrine were also explored by Plato in his first dialogues, especially in the Protagoras. First, the multiplicity of different manifestations of human excellence are thus reduced to the possession of a knowledge, a problem that was thoroughly explored in ancient literature and resulted, contemporarily, in the question of the unity of virtue. Secondly, the central role of knowledge in the comprehension of the ethical life requires the comprehension of the relation between knowledge and other admittedly fundamental aspects such as appetites and passions that are decisive to the human soul and crucial to determine one's actions. This latter point arises from the abundant observation in Plato's first dialogues, especially in the Protagoras, that knowledge is not only a necessary condition but also a sufficient condition to obtain and exercise virtue in such a way that no extracognitive element (such as passions and appetites) is able to interfere in the path of action indicated by knowledge. If knowledge of the good is what defines virtue and if it is hegemonic when present in the human soul, what role is left to passions and appetites in the ethics of the first dialogues? These two points are articulated in the doctrine that is exposed in the Protagoras, a dialogue that deepens and systematizes Socrates' theories discussed in the other dialogues from this period. Therefore, I intend to examine the relation between virtue and knowledge in the Protagoras. This work is divided in two parts: in the first, I deal with the problem of the unity of virtues; in the second part, I investigate the meaning of ethical intellectualism in view of the relation between knowledge and non-cognitive elements, and one particular virtue shall be examined: courage.