The goal of the study was to describe and analyze conceptual differences between the human capacity of knowing and the necessity to validate what has been given as knowing. The first condition is defined as gnosiology and the second is defined as epistemology. The two definitions of epistemology are contextualized in the general field of philosophy, in contrast with ontology (the fundamental nature of reality or being); logic (the rules of correct or right thinking); and axiology (ethics as human values, and aesthetics as human values for natural and artifactual things). The analysis is exemplified with Maine de Biran 's psychological theory. It provides a structure that is easy to understand and, unlike what occurred in the first half of the nineteenth century, it does not arouse great passion anymore.