Synthesized answer
Descartes states that good sense is the most equally distributed of all things among men because everyone believes they possess enough of it, and even those who are hard to please in other matters do not desire more good sense than they already have [1]. This widespread conviction suggests that the ability to judge correctly and distinguish truth from error, which is what good sense or reason is, is naturally equal in all individuals [1].
The diversity of opinions among people, therefore, does not stem from differences in their share of reason, but rather from the fact that they direct their thoughts in different ways and focus on different subjects [1]. While having a strong mind is important, the primary requirement is to apply it correctly [1]. Descartes believes reason is found complete in each individual, and differences are in accidental qualities, not in the fundamental nature or form of individuals within the same species [2].
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
er advancement in the investigation of Nature than has yet been made, with the reasons that have induced him to write. PART I Good sense is, of all things among men, the most equally distributed; for every one thinks himself so abundantly provided with it, that those even who are the most difficult to satisfy in everything else, do not usually desire a larger measure of this quality than they already possess. And in this it is not likely that all are mistaken the conviction is rather to be held as testifying that the power of judging aright and of distinguishing truth from error,…
rs in promptitude of thought, or in clearness and distinctness of imagination, or in fullness and readiness of memory. And besides these, I know of no other qualities that contribute to the perfection of the mind; for as to the reason or sense, inasmuch as it is that alone which constitutes us men, and distinguishes us from the brutes, I am disposed to believe that it is to be found complete in each individual; and on this point to adopt the common opinion of philosophers, who say that the difference of greater and less holds only among the accidents, and not among the forms…
osed to good morals, but to the circumstance that, originated by a single individual, they all tended to a single end. In the same way I thought that the sciences contained in books (such of them at least as are made up of probable reasonings, without demonstrations), composed as they are of the opinions of many different individuals massed together, are farther removed from truth than the simple inferences which a man of good sense using his natural and unprejudiced judgment draws respecting the matters of his experience. And because we have all to pass through a state of infancy to…
to imitate. The single design to strip one’s self of all past beliefs is one that ought not to be taken by every one. The majority of men is composed of two classes, for neither of which would this be at all a befitting resolution: in the first place, of those who with more than a due confidence in their own powers, are precipitate in their judgments and want the patience requisite for orderly and circumspect thinking; whence it happens, that if men of this class once take the liberty to doubt of their accustomed opinions, and quit the beaten highway, they will never be able to…
e more liable to error and the less capable of perceiving truth in very proportion as they are more subtle and lively. As to the opinions which are truly and wholly mine, I offer no apology for them as new,--persuaded as I am that if their reasons be well considered they will be found to be so simple and so conformed, to common sense as to appear less extraordinary and less paradoxical than any others which can be held on the same subjects; nor do I even boast of being the earliest discoverer of any of them, but only of having adopted them, neither because they had nor because they…