Plato, Descartes, Hume
1
In Plato's "Apology," Socrates defends himself against the charge of corrupting the youth by asserting that he does not claim to teach or have wisdom, unlike those who profess knowledge without truly possessing it. He argues that his purpose has merely been to question and examine the citizens of Athens to reveal their lack of wisdom and to prove incorrect the Oracle. This also relates to his claim that wisdom involves recognizing one's own ignorance. Socrates, however, ultimately believes that his awareness of his ignorance makes him wiser than those who falsely claim knowledge. Thus, by challenging the purported knowledge of others, he encourages critical thinking and self-examination among the youth, rather than corrupting them.
2
In the "Meditations," Descartes uses the method of doubt, i.e., questioning all beliefs that can possibly be doubted, to arrive at certainty. He questions all beliefs that could be false in order to find that one single truth upon which one may build reliable knowledge. He doubts external reality and then tackles consciousness itself. But because he has consciousness, he concludes I think, therefore I am. With confidence in his own existence, he proceeds to the conclusion that, since he did not make himself or reality, God must be the source of all creation, being the first cause of existence.
3
In the 3rd Meditation, Descartes argues for the existence of God by asserting that the idea of a perfect being must have a cause that is itself perfect, which he identifies as God. This argument is essential for his philosophical system because it helps to secure the reliability of clear and distinct perceptions, thereby allowing him to escape the radical doubt introduced earlier. God's existence guarantees that no evil demon is deceiving him, thus legitimizing his foundational truths and the external world.
4
According to Hume, the source of all knowledge is experience, derived from impressions (sensory experiences) and ideas (mental representations of impressions). This empirical approach underlies his skepticism about the existence of anything beyond immediate perception. Regarding personal identity, Hume argues that it is a fiction; there is no fixed self, only a bundle of perceptions that change constantly. This view challenges the notion of a persistent, unchanging identity by emphasizing the fluidity of self-conception based on changing experiences.
