Letter 9 (13) Spinoza to Oldenburg,
Letter 29a Spinoza to L. M. (Lewis Meyer),
Letter 70 (81) Spinoza to Tschirnhausen,
Letter 72 (83) Spinoza to Tschirnhausen, and
Letter 34 (21) Spinoza to Blyenbergh where he writes:
"...As regards Lewis Meyer's preface, the points which were still left to be proved by Descartes before establishing his demonstration of free will, are certainly there set forth; it is added that I hold a contrary opinion, my reasons for doing so being given. I shall, perhaps, in due time give further explanations. For the present I have no such intention.
I have never thought about the work on Descartes nor given any further heed to it,
since it has been translated into Dutch. I have my reasons, though it would be
tedious to enumerate them here. So nothing remains for me but to subscribe myself, &c."
In which some points relating to Being and its Affects are briefly explained.