In 1663 Spinoza published the only work to which he ever set his name... He had prepared a summary of the second part of Descartes' 'Principles of Ph… - Benedictus de Spinoza

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In 1663 Spinoza published the only work to which he ever set his name... He had prepared a summary of the second part of Descartes' 'Principles of Philosophy' for the use of a pupil... Certain of Spinoza's friends became curious about this manual and desired him to treat the first part of Descartes' work also in the same manner. This was done within a fortnight and Spinoza was then urged to publish the book, which he readily agreed to do upon condition that one of his friends would revise the language and write a preface explaining that the author did not agree with all the Cartesian doctrine... The contents... [included] an appendix of 'Metaphysical Reflections,' professedly written from a Cartesian point of view, but often giving significant hints of the author's real divergence from Descartes. ...'On this opportunity,' he writes to Oldenburg, 'we may find some persons holding the highest places in my country... who will be anxious to see those other writings which I acknowledge for my own, and will therefore take such order that I can give them to the world without danger of any inconvenience. If it so happens, I doubt not that I shall soon publish something; if not, I will rather hold my peace than thrust my opinions upon men against the will of my country and make enemies of them.' ...The book on Descartes excited considerable attention and interest, but the untoward course of public events in succeeding years was unfavourable to a liberal policy, and deprived Spinoza of the support for which he had looked. ...
If Spinoza had ever been a disciple of Descartes, he had completely ceased to be so... He did not suppose the geometrical form of statement and argument to be an infallible method of arriving at philosophical truth; for in this work he made use of it to set forth opinions with which he himself did not agree, and proofs with which he was not satisfied. We do not know to what extent Spinoza's manual was accepted or taken into use by Cartesians, but its accuracy as an exposition of Descartes is beyond question. One of the many perverse criticisms made on Spinoza by modern writers is that he did not understand the fundamental proposition cogito ergo sum. In fact he gives precisely the same explanation of it that is given by Descartes himself in the Meditations.