Schopenhauer's philosophy ‐ as a type of immanent metaphysics ‐ maintains that a priori knowledge of nature can be confirmed by empirical investigations. In the book Über den Willen in der Natur, Schopenhauer tries to show that modern biology has given a confirmation of his own philosophy of organic nature.That is the main topic of the article. The ‘appendix’ contents a selection of important literary reactions to Schopenhauer's inquiry concerning the relations between metaphysics and natural science.