"But since it is not easy to review all the connections together, and moreover, since our task is not so much to retain them in our memory as to distinguish them with, as it were, the sharp edge of our mind, we must seek a means of developing our intelligence in such a way that we can discern these connections immediately whenever the need arises"
— Descartes, René (1596-1650)
(Rule 6, p. 22)
See Opuscula posthuma, physica et mathematica (Amsterdam: P. and J. Blaeu, 1701).
Not published in Descartes' lifetime. Dutch translation in 1684; published in Latin in 1701.