Within the framework of epistemic foundationalism, Aristotle regards first principles as immediate starting points and as conditions for the possibility of demonstration. Yet the manner in which the mind attains these principles remains a contested issue in interpretations of his epistemology. Focusing on the negative dimension of Aristotle’s theory of knowledge, this paper asks: on what grounds does he reject both innatism and pure empiricism as adequate accounts of the origin of first principles? Through conceptual analysis and logical reconstruction of Aristotle’s arguments, grounded in his primary texts, the study shows that he dismisses the innateness of first principles because it conflicts with our awareness of demonstrative knowledge and generates problematic regressive consequences. Moreover, by distinguishing inductively derived universals from first principles, and by emphasizing that sense perception is essentially directed toward particular, here-and-now objects, Aristotle reveals the inability of sensory experience to secure strict necessity and absolute universality. Accordingly, Aristotle’s negative critiques do not merely refute two rival positions; rather, they establish first principles as conditions for the possibility of scientific knowledge and prepare the theoretical ground for positing a distinct cognitive faculty (nous). The originality of this paper lies in its systematic reconstruction of the negative dimension of Aristotle’s epistemology and in its careful differentiation between empirical universals and the foundational principles of science.