The text explores the philosophical reflection on the scientific concept of a 'fact,' which is founded upon two inseparable sources: sensory data and rational constructions. The author emphasizes that no conceptual construction can be considered conclusive without sensory verification, just as no sensory experience is sufficient on its own to establish a fact. A central thesis is that there is no sensory experience that is not co-constituted by reason; even the most basic perceptions are shaped by intellectual activity. The author rejects extreme empiricism, which assumes the existence of immediate sensations that are only subsequently processed by the mind. Since reason (or prejudices) penetrates all sensory functions, this intervention must be controlled through the extensive development of the intellectual component. Ultimately, the text asserts that for any fact to be validly established, it must be properly situated within a broader conceptual and theoretical framework. This approach necessitates continuous critical reflection on both sources of knowledge.