Whereupon I gladly take this opportunity to beg those who shall come after us never to believe that the things which they are told come from me unless I have divulged them myself; and I am in nowise astonished at the extravagances attributed to those old philosophers whose writings have not come down to us.  They were the greatest minds of their time, but have been ill-reported.  Why, I am sure that the most devoted of those who now follow Aristotle would esteem themselves happy if they had as much knowledge of nature as he had, even on the condition that they should never have more!  They are like ivy, which never mounts higher than the trees which support it, and which even comes down again after it has attained their summit.  So at least, it seems to me, do they who, not content with knowing all that is explained by their author, would find in him the solution also of many difficulties of which he says nothing, and of which, perhaps, he never thought.

Yet their method of philosophising is very convenient for those who have but middling minds, for the obscurity of the distinctions and principles which they employ enables them to speak of all things as boldly as if they had knowledge of them, and sustain all they have to say against the most subtle and skilful without there being any means of convincing them; wherein they seem to me like a blind man who, in order to fight on equal terms with a man who has his sight, invites him into the depths of a cavern.  And I may say that it is to their interest that I should abstain from publishing the principles of the philosophy which I employ, for so simple and so evident are they that to publish them would be like opening windows into their caverns and letting in the day.  But if they prefer acquaintance with a little truth, and desire to follow a plan like mine, there is no need for me to say to them any more in this discourse than I have already said.

For if they are capable of passing beyond what I have done, much rather will they be able to discover for themselves whatever I believe myself to have found out; besides which, the practice which they will acquire in seeking out easy things and thence passing to others which are more difficult, will stead them better than all my instructions.

But if some of the matters spoken about at the beginning of the “Dioptrics” and the “Meteors” [published with the “Discourse on Method”] should at first give offence because I have called them “suppositions,” and have shown no desire to prove them, let the reader have patience to read the whole attentively, and I have hope that he will be satisfied.

The time remaining to me I have resolved to employ in trying to acquire some knowledge of nature, such that we may be able to draw from it more certain rules for medicine than those which up to the present we possess.  And I hereby declare that I shall always hold myself more obliged to those by whose favour I enjoy my leisure undisturbed than I should be to any who should offer me the most esteemed employments in the world.