Excerpts of Letters to Joachim Roelants
They ought to be grateful to me as the first who has dared to attack man’s false opinions, to lay bare the extraordinary frauds of the Greeks, and to provide our contemporaries with an unusual opportunity for searching out the truth.  Such, however, is not the case, because Galen’s authority you will find many who, having glanced at my efforts only superficially and without investigation of the cadaver, still maintain that what Galen wrote is wholly correct.

The writings of many learned men comment my youthful efforts far more than they deserve and willingly confess that they prefer to put trust in their eyes rather than in Galen’s writings, nevertheless I understand that there are many who, although they agree that my work has virtue and credit me with ability beyond my merits, yet are angry with me for Galen’s sake.  Among them is Jacobus Sylvius, leading physician of our day, who, in a letter transmitted by your son, expressed his opinion very strongly even though he declared that he had not read my books De Humani Corporis Fabrica. Consequently you can easily gather what was in the letter I sent you from Nymwegen so that it might be transmitted to Sylvius by your son.  In that letter I replied to Sylvius, adding things here and there that, in my disturbed state of mind, seemed a proper reply, but most of them referring to anatomy, remarks by which the falseness of his assertions was revealed and by which my own position was explained.

Sylvius replied in his usual way, declaring that he did not consider himself of sufficient erudition or authority to desire to judge in such an important matter, but that nevertheless he would express his opinion briefly because I had asked for it.  After he stated that I had improperly criticized Galen, he asserted that what had offended him most of all was my bold declaration that Galen had not dissected human bodies, that he had only looked at the veins in the hands of living persons, and that he had copied his Use of Parts from the writings of others…He declared that he remains firmly convinced that Galen’s description of the human body is without error in every instance in which I claim that Galen’s description is partly or wholly incorrect or that he has been forgetful and explained the body’s function imperfectly or used faulty reasoning to support his doctrines.

Sylvius is the last one from whom I should have expected such an opinion…Nor can I accept his proposal that, if I withdraw my false statements regarding Galen and attribute them to my youthfulness and the influence of the Italians who oppose Galen, he will do his best during his lectures to conceal from his audience the fact that he does not approve of my work.  He wrote that he made this offer because he likes and respects me and wishes to keep my friendship, and because he feels that we could not remain friends if we were to disagree over Galen.  In order to frighten me still more, he added that even if he were to remain silent himself, others might disclose his true opinion of my work, for some of his students, whom he considers as very capable anatomists, are sharpening their pens against me because they are indignant that I should make remarks against Galen, master of all physicians.  Hence, he asked me what I wanted him to do for me in the matter, and of course he meant that I ought to desire to retract and so escape those sharp pens of his students…

I began my letter to Sylvius by saying that I was less upset by his remarks because I had seen many very learned physicians and philosophers who had been just as angry as him because I had said such things about Galen.  These men could not believe that the father of medicine had made such mistakes in the anatomical books he felt had been written with so much care and accuracy, the more so since it was a subject in which he had acquired greater authority than anyone else, even during his own lifetime.  Gradually, however, they began to change their attitude, and there was not one among them who, with the cadaver before him, could continue to defend Galen.  However reluctantly, they came to put more faith in their eyes than in the words of Galen.  It is my hope that eventually Sylvius, too, will change his mind as he reads through what I have written and that he will not deny me his good will and friendship.  However, as I wrote, whatever the case may be I should consider it as merely one of the misfortunes of mortals that must be borne, as I have not yet learned to speak counter to my own belief.

Furthermore, that which he criticized in me becomes greater very day.  That youthfulness with which Sylvius charges me has passed, but my increased years have not made me change my opinion.  I shall not mention how much I was hurt by the retreat that he offered me: the pretense that the Italians dislike Galen, because nowhere is Galen more respected and honored that in Italy.  this is fully proved by their publication of his works, even if they have not entirely discarded the Arabs and removed them from the medical curriculum.  I should certainly be guilty of the greatest impertinence if I were to accuse such learned men my kind friends to whom I am indebted, of being responsible for what he calls my error.  Those Italians, like Sylvius, usually opposed me, although I had never seen any of them put a hand to the cadaver before they first attended my dissections, and they are well aware that none of them was ever my instructor or helper in these matters.