Homeopathic medicine was the creation of a single person, Samuel Hahnemann, who graduated from a German medical school in 1779 and practiced the "healing arts" until 1843, first in Germany and then in Paris.  The theoretical underpinning of Hahnemann's new approach to health and vitality is that a healthy human being is inhabited by an integrated spirit or vital force. 

In Hahnemann's words, "The vital force that animates the healthy body, rules with unbounded sway, and  retains all the parts of the organism in admirable, harmonious, vital operation . . . so that our indwelling, reason-gifted mind can freely employ this living, healthy instrument for the higher purpose of our existence." Diseases and ailments (other than those inflicted by physical blows to the body) are supposedly not caused by material substances.  Rather, as Hahnemann wrote, "when a person falls ill, it is only this spiritual vital force, everywhere present in his organism, that is primarily deranged by another dynamic influence hostile to his life."  So how does a patient overcome disease? By consuming a positive spiritual medicine that "occupies precisely the seat hitherto occupied by the derangement." 

In other words, the demonic element of the vital spirit must be replaced by the angelic element of the natural homeopathic remedy. 

Early in his career, Hahnemann was rightly disturbed by many European medical practices -- including bloodletting with leeches, poison-induced vomiting, and acid-induced skin blisters -- that made patients sicker than they were before treatment.  In 1790, he came across a manuscript (while plying his second trade as a translator of Latin into German) from a Peru-based missionary describing the remarkable malaria-curing ability of powder from the bark of Cinchona (a species of South American evergreen tree).  Others had attributed the cure simply to the caustic taste of the bark, but Hahnemann realized that more caustic substances did not elicit similar cures, and so this simple explanation was false.  Curiosity drove him to do what other physician-scientists of his day did  -- self-experimentation on the consequences of ingesting Cinchona powder. After several days, Hahnemann had the epiphany of his life when he became ill with fever-like symptoms similar to those caused by malaria.

Through the similarity in symptoms evoked by a single disease and its curative agent -- which are not nearly as similar as he imagined -- Hahnemann came to the conclusion that cures to every kind of human disease could be obtained from substances that elicited the same set of symptoms in otherwise healthy people.  This assertion, which he called the "Law of Similars," with the adage "likes are cured by likes," became the empirical basis for practicing his newly invented homeopathic (literally similar-suffering) system of medicine. Homeopathy was presented in contrast to what Hahnemann referred to as allopathic treatment with medicines that produced effects opposite to the disease they were meant to cure. 

Over the next 20 years, Hahnemann traveled far and wide with his students and family members to evaluate the effects of ingesting plant and animal-derived substances from as many sources as he could find.  When a substance produced sensations similar to the symptoms of any known disease, it was added to his list of homeopathic medicines. However, as a good physician, Hahnemann didn't want to make people sicker than they were already, so he diluted a drop of the symptom-causing substance over and over again into alcohol or water with vigorous shaking and rubbing at each stage. (For insoluble substances, dilutions were made into powdered sugar.) 

Through this process, he claimed, medicines became more potent or "highly dynamized."  In 1810, Hahnemann published the first edition of his masterpiece, Organon der Heilkunst (Organon of Medicine), which elaborated the philosophy of homeopathy and the arguments for its validity in 271 aphorisms (the number changed in each subsequent edition). The sixth and last edition, written in 1842 but not published until 1921, is still the basic text and defining source for homeopathic practitioners worldwide today.

Since disease is spiritual, not material, a cure is best effected when the medicine contains no interference -- no material substance -- from the original curative agent. The greater the dilution, the stronger the medicinal spirit becomes. A dilution of 10100 (equal to the digit one followed by 100 zeros) is spiritually potent, but a dilution of 10400 (a number equal to all the particles in at least  10200 universes as big as our own) is even more potent.  Hahnemann was adamant that material medicines couldn't cure disease, but he accepted mesmerizers as a valid homeopathic alternative. 

Mesmerizers were "strong-willed, well-intentioned" people with an overabundance of vital force, some of which could be donated to a sick person whose own vital force was deficient.  However, to maintain their abilities, mesmerizers had to avoid sexual intercourse and masturbation so that "all the fine vital spirits that would otherwise  be employed in the production of the semen, are ready to be communicated to others."

Why was Hahnemann so confident in his understanding of health and disease? First, he argued, no visible agent can be seen in association with malaria, syphilis, or smallpox, so their causes must be spiritual. (Within a century, Pasteur's germ theory of infection would invalidate this claim.)  Second, when a bar of iron is rubbed repeatedly in the same direction with a metal file, it can gain more and more "magnetic power," without any change in its mass.  "In the same way," Hahnemann wrote, "shaking a medicinal substance develops the medicinal powers hidden within . . ." (Within a century, physicists would explain magnet formation in terms of aligning atomic axes inside a metal.) Third, no material substance had been identified that was responsible for the malaria-curing properties in Cinchona bark. (In 1820, during his lifetime, quinine was discovered as the active chemical inside the bark. He never acknowledged this finding.) 

Hahnemann had no use for scientific method or theory. He belittled scientifically-oriented physicians in writing, "How the vital force causes the organism to . . . produce disease, it would be of no practical utility to the  physician to know, and will forever remain concealed from him. . ."  His faith in the truth of his "law" likes are cured by likes was so great and absolute, he saw no need to test the effectiveness of homeopathic remedies on actual sick people. Homeopathic remedies are still subjected to "provings," (their term) only by determining whether they cause disease-like sensations in a healthy person when used at full strength, not by determining whether they actually have any curative effects in diluted form on an unhealthy person.  Meanwhile, so-called allopathic medicines that produce effects opposite to the disease -- like aspirin's relief of pain -- are rejected because they are not in harmony with the body's vital spirit.

Homeopathy is particularly appealing to Church-rejecting post-Christian Westerners who embrace a spiritual sense of nature that is under attack from capitalistic agriculture and paternalistic medicine.  The post-Christian worldview is particularly widespread in France and Germany where pharmacies typically give homeopathic remedies as much shelf space as real medicines.