René Descartes - Rules for the Direction of the Mind
9 Sourced Quotes
No more useful inquiry can be proposed than that which seeks to determine the nature and the scope of human knowledge.... This investigation should be undertaken once at least in his life by anyone who has the slightest regard for truth, since in pursuing it the true instruments of knowledge and the whole method of inquiry come to light. But nothing seems to me more futile than the conduct of those who boldly dispute about the secrets of nature... without yet having ever asked even whether human reason is adequate to the solution of these problems.
We must believe that all the sciences are so interconnected, that it is much easier to study them all together than to isolate one from all the others. If, therefore, anyone wishes to search out the truth of things in serious earnest, he ought not to select one special science; for all the sciences are cojoined with each other and interdependent..
But as I considered the matter carefully it gradually came to light that all those matters only were referred to Mathematics in which order and measurement are investigated, and it makes no difference whether it be in numbers, figures, stars, sounds or any other objects that the question of measurement arises.