Introduction

René Descartes stated in Discourse on the Method that “good sense is the most evenly distributed thing in the world.” With this assertion, he established a principle of fundamental equality among humans: everyone possesses reason. Reason thus becomes not only what distinguishes humans from animals but, above all, what grounds human dignity. To think, then, is to exist; cogito ergo sum. The existence of the subject is rooted in the capacity to reason.

The Difficulty of Universality of Reason

The history of thought shows that the universality of reason, so appealing in theory, confronts diverse uses and conclusions. If all humans have reason, why do they not reason in the same way? Why do interpretations multiply and conflict over identical facts, questions of justice, or moral issues? Where does this plurality, in what should be universal, come from? Kant provides an essential clarification. In Critique of Practical Reason, it is not just about noting that humans possess reason but reminding them that they must exercise it autonomously. To be reasonable is not merely to reason; it is to give oneself a universal moral law. Reason thus becomes the foundation of ethics: it both enables freedom and grounds moral law. Through it, humans no longer need transcendence to live in immanence; they become lawmakers of their own conduct.

Human Impartiality

Yet this autonomy, the greatest virtue of reason, is also its limitation. When everyone exercises reason freely, each does so according to their experience, interest, or cultural horizon. Here lies the paradox: reason is universal in essence but singular in practice. Its intensity is not equal in all; it is a power to cultivate, educate, and direct. Thus, when two people reason differently about the same legal situation, it is not because truth itself divides, but because their respective reasoning is influenced by passions, values, or perspectives. Spinoza aptly observed: “Men think themselves free because they are ignorant of the causes that determine them.” Reason is often disrupted by desire, self-interest, or fear. Each interprets truth in their favour—not because truth changes, but because their perspective is distorted. The plurality of responses to the same fact is therefore not a sign of the absence of truth but of humanity’s search for it. Reason, though common, unfolds within singular contexts; this tension between universality and particularity defines the human condition.

Conclusion

Ultimately, the question is not whether all humans possess reason—they do—but whether they exercise it truly rationally, that is, disinterestedly, freely, and morally. Where reason becomes an instrument of power, it loses its light; where it remains open to the universal, it illuminates the path of justice and truth.