Baruch Spinoza 
Treatise on the Emendation of the Intellect [EPUB ebook] 

This Treatise on the Emendation of the Intellect etc., which we give you here, kind reader, in its unfinished [that is, defective] state, was written by the author many years ago now. He always intended to finish it. But hindered by other occupations, and finally snatched away by death, he was unable to bring it to the desired conclusion. But since it contains many excellent and useful things, which–we have no doubt–will be of great benefit to anyone sincerely seeking the truth, we did not wish to deprive you of them. And so that you would be aware of, and find less difficult to excuse, the many things that are still obscure, rough, and unpolished, we wished to warn you of them. Farewell.