“Good sense is the most evenly shared thing in the world [...] It indicates rather that the capacity to judge correctly and to distinguish the true from the false, which is properly what one calls common sense or reason, is naturally equal in all men, and consequently that the diversity of our opinions does not spring from some of us being more able to reason than others, but only from our conducting our thoughts along different lines and not examining the same things. For it is not enough to have a good mind, rather the main thing is to apply it well.”

In this passage, Descartes is making the claim that good sense—the ability to render identical the objects of our experience with the ideas we have of those objects in our minds—is a common human attribute. For Descartes, differences between individuals arise not in some who lack such an ability but rather in the chain of reasoning used by various individuals. This is why Descartes claims that it is not enough to simply be capable of good sense and the correct use of reason; what is key is the correct application of our mind, so that the objects of our experience match up with the ideas we have of them in our mind.

“I shall say nothing about philosophy, except that, seeing that it has been cultivated by the very best minds which have ever existed over several centuries and that, nevertheless, not one of its problems is not subject to disagreement, and consequently is uncertain, I was not presumptuous enough to hope to succeed in it any better than others, and seeing how many different opinions are sustained by learned men about one item, without its being possible for more than one ever to be true, I took to be tantamount to false everything which was merely probable. As for the other sciences, in so far as they borrow their principles from philosophy, I consider that nothing solid could have been built on such shifting foundations; and neither the honour nor the material gain held out by them was sufficient to induce me to study them.”

In this passage, Descartes is describing his experience of studying philosophy at university. This experience was formative for Descartes precisely because it taught him that the history of philosophy is populated less with answers that are absolutely and irrefutably true and more with a wide variety of differing positions, even with respect to a single topic. In this regard, says Descartes, we should not look to philosophy as it is taught in the university to provide us access to a true understanding of ourselves, God, and the world, since academic philosophy itself cannot even settle upon an agreed-upon solution to key philosophical problems.