Descartes, Rene'(1596-1650), great mathematician and
philosopher, planned to give a universal method to solve
problems but he left unfinished his Rules for the direction
of the Mind. The fragments of this treatise, found
in his manuscripts and printed after his death, contain
more--and more interesting--materials concerning the 
solution of problems than his better known work 
Discours de la Methode Although the "discourse" was very
likely written after the "Rules."  The following lines of
Descartes seem to describe the origin of the "Rules": "As 
a ***** man, when I heard about ingenious inventions, 
I tried to invent them by myself, even without reading
the author. In doing so, I perceived, by degrees, that I 
was making use of certain rules."