Here a bit of what Yates has to say on Descartes:

Descartes also exercised his great mind on the art of memory and how it might be reformed, and the mnemonic author who gave rise to his reflections was none other than Lambert Schenkel. In the Cogitationes privatae there is the following remark:

On reading through Schenkel’s profitable trifles [in the book De arte memoria ] I thought of an easy way of making myself master of all I discovered through the imagination. This would be done through the reduction of things to their causes. Since all can be reduced to one it is obviously not necessary to remember all the sciences. When one understands the causes all vanished images can easily be found again in the brain through the impression of the cause. This is the true art of memory and it is plain contrary to his [Schenkel’s] nebulous notions. Not that his [art] is without effect, but it occupies the whole space with too many things and not in the right order. The right order is that the images should be formed in dependence on one another. He [Schenkel] omits this which is the key to the whole mystery.

I have thought of another way; that out of unconnected images should be composed new images common to them all, or that one image should be made which should have reference not only to the one nearest to it but to them all – so that the fifth should refer to the first through a spear thrown on the ground, the middle one through a ladder on which they descend, the second one through an arrow thrown at it, and similarly the third should be connected in some way either real or fictitious.14

Curiously enough, Descartes’s suggested reform of memory is nearer to ‘occult’ principles than Bacon’s, for occult memory does reduce all things to their supposed causes whose images when impressed on memory are believed to organize the subsidiary images. Had Descartes consulted Paepp on ‘detecting’ Schenkel15 he would have known of this. The phrase about the ‘impression of the cause’ through which all vanished images can be found might easily be that of an occult memory artist. Of course Descartes is certainly not thinking on such lines but his brilliant new idea of organizing memory on causes sounds curiously like a rationalization of occult memory. His other notions about forming connected images are far from new and can be found in some form in nearly every text-book.

It seems unlikely that Descartes made much use of local memory, which, according to quotations in Baillet’s Life , he neglected to practise much in his retreat and which he regarded as ‘corporeal memory’ and ‘outside of us’ as compared with ‘intellectual memory’ which is within and incapable of increase or decrease.16 This singularly crude idea is in keeping with Descartes’s lack of interest in the imagination and its functioning. Rossi suggests, however, that the memory principles of order and arrangement influenced Descartes, as they did Bacon.

Both Bacon and Descartes knew of the art of Lull to which they both refer in very derogatory terms. Discussing false methods in the Advancement , Bacon says:

There hath been also laboured and put into practice a method, which is not a lawful method, but a method of imposture; which is, to deliver knowledges in such a manner, as men may speedily come to make a show of learning who have it not. Such was the travail of Raymundus Lullus in making that art which bears his name…

And Descartes in the Discours de la méthode is equally severe on the Lullian art which serves but to enable one ‘to speak without judgment of those things of which one is ignorant’.18

Thus neither the discoverer of the inductive method, which was not to lead to scientifically valuable results, nor the discoverer of the method of analytical geometry, which was to revolutionize the world as the first systematic application of mathematics to the investigation of nature, have anything good to say of the method of Ramon Lull. Why indeed should they? What possible connexion can there be between the ‘emergence of modern science’ and that medieval art, so frantically revived and ‘occultized’ in the Renaissance, with its combinatory systems based on Divine Names or attributes. Nevertheless the Art of Ramon Lull had this in common with the aims of Bacon and Descartes. It promised to provide a universal art or method which, because based on reality, could be applied for the solution of all problems. Moreover it was a kind of geometrical logic, with its squares and triangles and its revolving combinatory wheels; and it used a notation of letters to express the concepts with which it was dealing.

When outlining his new method to Beeckman, in a letter of March 1619, Descartes said that what he was meditating was not an ars brevis of Lull, but a new science which would be able to solve all questions concerning quantity.19 The operative word is, of course, ‘quantity’, marking the great change from qualitative and symbolic use of number. The mathematical method was hit upon at last, but in order to realize the atmosphere in which it was found we should know something of those frenzied preoccupations with arts of memory, combinatory arts, Cabalist arts, which the Renaissance bequeathed to the seventeenth century. The occultist tide was receding and in the changed atmosphere the search turns in the direction of rational method.