International Encyclopedia of Systems and Cybernetics

In this famed piece of scientific philosophy, DESCARTES (1596-1650) enounces as follows the four "precepts" to "conduct one's reason" in a correct way:

"The first was never to accept anything for true which I did not clearly know to be such; that is to say, to avoid carefully precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.

"The second is to divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.

"The third, to conduct my thoughts in such order that by commencing with objects the simplest and easiest to know, I might ascent by little and little, and, as it where, step by step, to the knowledge of the more complex; assigning in thought a certain order even to those objects which in their own nature do not stand in a relation of antecedence and sequence.

"And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted" (S. CUMMINS & R.L LINSCOTT's translation, 1947, p.175-6).

These concepts have dominated scientific research for more than three centuries and led to considerable progress, through an ever increasing specialization.

However, the following caveats should be taken into account:

- DESCARTES' concept of evidence is subjective and implicitely based on an ontological absolute. This remains largely true even when the "evidence" is inter-subjectively accepted through a wide consensus.

- While "dividing the difficulties" may indeed be useful in many cases, it easily leads altogether to severing links and interactions, i.e. destroy the very nature of complex systems.

- While DESCARTES third precept about climbing back toward "the more complex" is sound, he does not give any method to reconstruct the severed links.

- His "complete enumerations and general reviews" can never give a complete security that "nothing has been omitted", since he gives no criterion for evaluation on this supposed completeness.

Even if the historical usefulness of Cartesian method has been massively demonstrated, the above objections explain why reductionism is insufficient for the satisfactory study of complex systems.