Samuel Hahnemann, in the preface to the second edition of his Organon of Medicine, critically addressed the speculative nature of prevailing medical theories, which he termed "Theoretical Medicine." In this context, he used the term "**a priori**" to describe these theoretical constructs that were often based on abstract reasoning and assumptions not derived from empirical observation and experience. Hahnemann advocated for a system of medicine grounded in careful observation of nature and the effects of drugs on healthy individuals, as demonstrated through homeopathic provings.