It is not enough to have a good mind. The main thing is to use it well.

This line is widely attributed to René Descartes and is commonly linked to the opening of his 1637 Discours de la méthode (Discourse on the Method). In that work, Descartes introduces his project of reforming knowledge by adopting a disciplined method of reasoning rather than relying on inherited authorities. The remark fits the essay’s early emphasis that “good sense” (reason) is broadly distributed among people, but that errors arise from how we direct our thinking. In context, Descartes is setting up a practical, methodological program: intellectual excellence depends less on native brilliance than on the correct use and ordering of one’s mind through methodical doubt, clear ideas, and careful inference.

The quote distinguishes possession of intelligence from the disciplined practice of thinking. Descartes suggests that raw mental capacity is insufficient; what matters is method—how one evaluates evidence, checks assumptions, and proceeds step by step. The line also carries an ethical undertone: responsibility attaches to the use of reason, not merely to having it. In a Cartesian frame, “using the mind well” means aiming at clarity and distinctness, resisting haste and prejudice, and submitting beliefs to rigorous scrutiny. The enduring appeal of the sentence is its democratic implication: sound judgment is less a gift than a skill, cultivated through habits of careful reasoning.