In order to grasp the role that a philosopher plays in the history of philosophy and to fully comprehend "what" he says, we must first understand "why" the philosopher says all this; which questions he keeps him awake by insistently demanding answers, in short, what the philosopher's "problem" is. As a thinker, with one hand reaching out to the Middle Ages and the other to modernity, Descartes witnessed the 17th century, which can be called the age of revolutions and crises. As a matter of fact, his philosophical system reflects the spirit of the period in every aspect and becomes understandable only in the light of this background. The aim of this study is to re-evaluate the founding principles of Cartesian metaphysics by taking into account the philosopher's genuine problem and ultimate purpose, and ultimately to show that the dualism of substance emerged as a necessary consequence of the project of making room for human mind, free will, and morality.