Hahnemann was the child of his time, grown up in the age of romantic mysticism. He was a hard polemist with colleagues, opponents and even his own followers if they did not accept enthusiastically all his hypotheses. However we must also acknowledge some merits, that even his fiercest adversaries recognized and that explain the success he reached in his late maturity. Samuel Hahnemann's merits must be looked at in the context of XVIII century medicine, whose defects and faults he clearly understood and criticized. Hahnemann did not show a comparable understanding of the worths of XVIII century medicine and completely missed the revolution of pathology that was unfolding at the time, suffice it to say that he graduated shortly after the publication of Morgagni's De sedibus and died one year after the publication of von Rokitanski's monumetal treatise on morbid anatomy.

Between the XVII and the XX century medicine underwent a slow revolution: the discoveries of the anatomists and physiologists of the Renaissance [1], the Galenic tradition had been largely disproven, but the new medical science did not imply a significant improvement of the available therapies. Indeed at the beginning of the XVIII century physicians were aware that their old theories were inadequate or false (and the new ones incomplete) but could only use the very same drugs and remedies in use since the greco-roman age. Pharmacology was not only obsolete with respect to physiology, but illogically anachronistical: it had been demonstrated largely ineffective, yet there was nothing better to substitute for it. During the XVIII century pathology became the most important amongst the medical sciences [2], but this made pharmacology even more obsolete, since the autopsies demonstrated lesions that no known drug could heal. Many physicians did acknowledge this condition [3].

Effective therapies available at the time include quinine (cinchona bark) for malaria, lemon juice for scurvy, digitalis for heart failure, opium as an analgesic and narcotic. Other available therapies are weak, e.g. vegetable diuretics and laxatives, and many are frankly damaging, e.g. blood-letting by venesection or leeches.
Hahnemann recognized very early during his medical practice that a great deal of the available therapies were either useless or damaging, and harshly criticized these methods that were often applied with such diligence to endanger the life of the patient. He also criticized the gross pharmacology of his times, that often had very imprecise notions about its drugs, and proposed an empirical approach based on the proving of drugs, the procedure of recording systematically the effects that each drug caused in healthy volunteers. The idea of the proving was wrong, since the effect observed on the healthy volunteer may be completely unrelated to the therapeutical action of the drug; e.g. quinine is toxic to the parasite that causes malaria and any effect on the healthy volunteer, whose organism does not host the parasite, is a collateral effect, utterly irrelevant to the desirable action of the drug. However Hahnemann's practice was a clear progress with respect to the indiscriminate usage of active substances whose effects were known to a very limited extent. Many physicians of the XVIII century, even among Hahnemann's critics, recognized that the proving was a valuable improvement over the methods of classical pharmacology [4].

Before the discovery (or invention) of homeopathy Hahnemann devoted considerable effort to the promotion of personal and social hygiene. He recognized that the cities of his times were unhealthy, the dwellings poorly areated and dirty, the food and water supplies unsatisfactory. He tried to formalize his suggestions and advices in some booklets, the most relevant of which is probably The Friend of Health (1795). Unfortunately Hahnemann's advice was based more on common sense and practical experience than on effective scientific investigation: e.g. he thought (and wrote in 1830) that cholera was trasmitted through the air and the personal belongings of the people infected, rather than by contaminated water, as J. Snow demonstrated only twenty years later.
On the occasion of the cholera epidemics of 1830-31, Hahnemann participated to the controversy between the physicians who attributed the disease to a "miasma" (i.e. to a negative atmospheric influence) and those who favored the hypothesis of interhuman transmission (contagion) [5]. Hahnemann was on the (right) side of the contagionists, and his position is quite remarkable since it contradicts several hypoteses of homeopathy: e.g. he had always maintained that the disease had no material bases and was a purely dynamic perturbation of the vital force, but in his writings on cholera he attributes the disease to materially existing microorganisms [6]. May be Hahnemann meant that the vital force of the germs was responsible for the perturbation of the vital force of the patient, but even with this assumption the hypothesis reamins atypical for homeopathy and contradicts his former writings. Indeed the american homeopath James Tyler Kent was convinced that the correct interpretation of Hahnemann's theory was exactly the opposite and taught that germs are innocuous.

We may also remark Hahnemann's enlightened positions on the treatment of psychiatric patients, for whom he recommended humanity and respect, thus refusing the often inhumane coercitive tretaments in use at the time. Hahnemann's specific experience in psychiatry is rather limited: in 1792-93 he was summoned in the small village of Georgenthal by the duke von Sachsen-Gotha to treat a sigle patient, the former cancellor Klockenbring. Since the hospitalization of psychiatric patients was expensive Klockenbring was the only inpatient at Georgenthal, and when he recovered and was able to resume his everyday life, Hahnemann's experience as a psychiatrist came to an end.
Hahnemann's sensible recommendations on the treatment of psychiatric patients, and his reproach of the moral and social stigmates associated to mental diseases were not unheard of in XVIII century Europe: indeed the same concerns were more strongly expressed by the French psychiatrists, as a consequence of the then recent revolution. The reformation of psychiatric institutions during the XVIII century is thus rightly credited to Philippe Pinel, whose lifelong work as a psychiatrist greatly surpasses Hahnemann's contributions.

In conclusion we notice that Hahnemann wrote on many medical subjects and published hypotheses and recommendations that are not obviously connected with the main endeavour of his life, homeopathy. He appears in these writings as an illuminated and conscientious physician, able to accept innovations and to refuse the errors of a long standing tradition.


SYMPTOMS, long before Hahnemann, were considered clues to the diagnosis. The subjective symptoms referred by the patient, spontaneously or under the questioning by the physician, and the signs of the disease that the physician finds during the physical examination, suggest one (or more) diagnostic hypotheses. Therapy is decided after the diagnosis. Nowadays we added a great number of diagnostic tests and laboratory analyses, and nosography has improved enormously, but the logic of the procedure has not significantly changed. Galen in the II century a.C. had compared the symptoms to the traces of the hare, that the hunter follows to find his prey (the disease; the diagnosis) and derided those contemporary physicians who believed that the symptoms exhausted the concept and definition of disease, by asking ironically whether a hare were made out of traces [7]. Much later Rene' Laennec (1781-1826) wrote that in the absence of a diagnosis no rational therapy can be prescribed [8].
To Hahnemann the symptom was at the same time more and less than it was thought and taught by the classical medical school, but his ideas were confused and self-contradictory. To understand, and to explain Hahnemann's thought requires to interpret a great deal of speculations, most often unfounded; but to avoid this enterprise means to continue the confusions of modern homeopaths, who are in general less rigorous than their master.
I shall discuss below the following points of Hahnemann's theory:
the the relationships between the symptom and the disease;
primary and secondary symptoms;
the study of the symptoms induced by homeopathic remedies;
the hypotheses of modern homeopaths;

Hahnemann did not refuse or avoid the diagnostic cathegories of his time and several diseass are named in the Organon: e.g. malaria (ague), scurvy, rickets, smallpox, etc. [see, as an example Organon, VI ed., par.38]. Diagnosis implies not only that the symptoms are correctly identified, but also that the whole of them, or at least the significant ones (the syndrome), are assigned to a cathegory (the disease). Thus Hahnemann by naming the malaria or the smallpox implicitly accepts the current opinion that these are different, precisely identified disases (as successive research demonstrated beyond any reasonable doubt).
In his theoretical speculations, however, Hahnemann suggested that diagnosis is arbitrary and that any group of symptoms can show up (i.e. that it is impossible to classify the syndromes), and even that an incompletely homeopathic theory (i.e. based on a remedy that reproduces only some of the symptoms of the patient) cures only part of the symptoms [
9]. This hypothesis contradicts the very concepts of disease and diagnosis, and it is evident that it is impossible to cure half a malaria or two thirds of a scurvy. Thus Hahnemann accepts and does not accept the conventional nosography.
Hahnemann thought that all diseases belong to just a single cathegory, the perturbation of the vital force; symptoms are the observable manifestation of this condition. According to this concept the symptom is not the clue to the diagnosis, but the disease itself, or at least that part of the disease that the patient and the physician can directly perceive:
"It is clear that human diseases are nothing but groups of certain symptoms and that they are destroyed and changed into health (the process of all true cure) by means of medicinal substances, but only by those that can artificially produce similar disease symptoms." Organon, VI ed., par.71.

"... all diseases are only dynamic disturbances of the vital principle and are not caused by anything material ..." Organon, VI ed., footnote to par. 282; on the same subject see also the arguments against pathology and morbid anatomy, par.74 and is footnotes.

Since the spiritual component of the disease (he perturbation of the vital force) is inseparable from its material counterpart (the totality of the symptoms), without the mediation of anatomical lesions, Hahnemann believes that curing all the symptoms implies to cure the disease itself:
"To change diseases into health the only thing that must be removed is the totality of the subjective and objective symptoms." Organon VI ed., par.22

We can summarize, and try to reword more rigorously, the above hypotheses by stating that conventional medicine considers the symptoms as caused by anatomical and functional lesions, and the disease as a complex entity made up of several discrete events linked by causal relationships (not necessarily deterministic), whereas Hahnemann considered the disease a unitary process. Galen had thought that the relationship between the disease and its symptoms was one of etiological causation (i.e. the disease and its symptom were different events, and the former was the cause of the latter), whereas Hahnemann believed that the symptom were linked to the disease by ontological causation (i.e. only one event existed of which the symptom was the surface and the perturbation of the vital force the core).
Recording the totality of the symptoms was of paramount importance to Hahnemann, who accused contemporary physicians of concentrating on just one or a few predominant symptoms and neglecting the others (a concept that modern homeopaths have modified to pretend that homeopathy treats "the patient", whereas conventional medicine treats "the disease" or "the altered laboratory tests"). Hahnemann's point is again part of the history of medicine, and refers to the distinction between "propria" and "communia".

Hahnemann, who had a remarkable acquaintance with contemporary and classical medical literature and was a skillfull observer, distinguished two types of symptoms:
PRIMARY SYMPTOMS, that express the perturbation of the vital force due to the disease;
SECONDARY, or reactive, SYMPTOMS due to the reaction of the vital force that opposes to the perturbation and tries to heal the disease.
We can now precisely define the causes of many symptoms and often we can recognize at the same time the consequences of the anatomical lesion and the reaction of the organism. Even though most symptoms hav at the same time primary and secondary components, Hahnemann's idea is still valuable, at least from a theoretical point of view. Hahnemann further thought that as a general rule, secondary symptoms were exactly the opposite of primary ones, and proposed several examples, of which I report just one. When a limb is immersed in cold water and then pulled out, the initial lowering of the temperature (the primary symptom) is rapidly followed by on increase of the blood flow and the temperature (the reaction or secondary symptom) [
Primary and secondary symptoms are also present in the intoxications, and in the homeopathic therapy (that Hahnemann considers akin an intentional intoxication), and Hahnemann explains that when studying the symptoms induced by homeopathic remedies (the so called "proving") it is important to list only primary symptoms, since these only are relevant to the choice of homeopathic therapy: i.e. a remedy is homeopathic to the disease of a patient only if the primary symptoms it induces in the healthy are similar to the primary symptoms of that patient. The idea that secondary symptom are scarcely relevant to the choice of the remedy logically follows from the vitalistic premise since the physician controls the iatrogenic disease, and not the reaction of the vital force of his patient.

In parallel with the above distinction, Hahnemann applied another, that between symptoms that are typical of the patient and symptoms that are typical of the disease. The former correspond to the propria of classical medicine, the latter to the communia (see the preceding page). Hahnemann attributes the greatest importance to the propria since he believes that the communia are poorly informative. The result is a great emphasis on the INDIVIDUALIZATION of the therapy, but also a great deal of arbitrariness since the propria may extend and contract according to the subjective judgement of the homeopath, and may include feelings, dreams, and thoughts.

In the XVIII century the effects of even the most common drugs was very imprecise: the specific of some drugs effect was empirically known (e.g. Cinchona for malaria and lemon juice fopr scurvy); those of other drugs were inferred from their action on the healthy (e.g. laxatives); and many drugs were used only on the basis of tradition. Hahnemann's theory stated that the effect of drugs was to be systematically explored in the healthy subjects by means of experiments (so called "provings") and many physicians felt that this were a very significant improvement. Not without reason Hahnemann was proud of homeopathic provings that were proof of the scientificity of his doctrine. However, in a short time, homeopathic provings became a double edged sword, and were criticized. The quarrels that Hahnemann entered in against his physicians colleagues were indefensible even for his biased biographer
Hahel [11], and made things worse. On the one hand the provings, carried out in the absence of any controls and under the assumption that every single sensation experienced by the prover was to be attributed to the drug he was testing, produced interminable and heterogeneous lists of symptoms and sensations, that defied credibility. On the other hand Hahnemann and his followers added to the lists of the symptoms reported by the healthy provers those present in patients that had been cured by the remedy(so called "clinical proving"). Since the physicians were aware that in many instances healing was spontaneous, and occurred also in the absence of any therapy, just because of the vis medicatrix naturae, clinical provings were unacceptable and implied that "nothing at all" was amongst the most powerful poisons, capable of producing a wealth of symptoms. At the end of the XIX century the lists of symptoms attributed to each homeopathic remedy were so complex and confused that the british homeopath R. Hughes tried to rethink the whole matter, escluding the symptoms coming from clinical provings and the less credible among those from the normal provings [12]; but his contemporaries did not follow and his work is today almost forgotten.
At present the homeopathic materia medica is confuse to say the less: the symptoms often include those from clinical provings, and some remedies are attributed over 1000 of them. Moreover, double blind trials (in which the prover does not know whether he is assuming the remedy or a fake pill) have demonstrated that neither lay subjects not homeopaths are able to identify the remedies. Finally Hanemann's original hypothesis of the similes proved wrong: in the great majority of the cases the therapeutical effect of a drug is independent of the symptoms it induces in the healthy prover [13].

Since vitalism is today closer to witchery than to biology, homeopaths have essentially but silently eliminated this hypothesis from their theory, and have used as a replacement less compromising concepts such as the self-regulatory mechanism of physiology (so-called
wisdom of the body), or the wholeness of the organism [15]. Needless to say, these concepts are taken from conventional science, trivialized and renamed; in their original form (homeostasis; emergent properties of the organism) they are much more precise. The main point, however, is that the modern versions or substitutes of the vital force do not possess those spiritual qualities that Hahnemann attributed to it and cannot logically justify many of the original deductions: e.g. the therapeutical disease or the law of the infinitesimals.
Within this simplified version of homeopathy, the only relevant symptoms are those called secondary by Hahnemann; and indeed many contemporary homeopaths try to eliminate the primary symptoms altogether and to state that all symptoms are secondary (i.e. reactive):

[The law of similars] "makes more sense, however, when symptoms are viewed as attempts on the part of the body to heal itself." [Gray, 2000, p.9].

Hahnemann, of course, did not think that all symptoms were "attempts of the body to heal itself", a definition that can only refer to some secondary symptoms; indeed he did not even esplicitly state that all secondary symptoms have therapeutical value, for, if they had, the necessity of substituting the natural with the iatrogenic disease would fade off. Gray (who follows preceding homeopaths) rewrites the theory in a simpler and more rigid form: symptoms are attempts to heal and therapy by similes is intended to stimulate and to strengthen them.

It may seem that the change is a minor one: after all the new theory is superficially more plausible than the original and saves the law of the similes. there are two reasons why this appeasement is to be refused:
1) It is not true that all symptoms are attempts of the body to heal itself, on the contrary they often kill the patient: on this point Hahnemann was a much better observer than his followers. To make just a few examples: convulsive fits are not attempts to stop a cerebral hemorrage; loss of the teeth does not heal the scurvy; pain does not block the progression of tabes or porphyria or whatever other disease and so on.
2) As the homeopath R. Hughes had already made clear at the end of the XIX century, while criticizing a similar hypothesis, Hahnemann thought that the law of the similes was to be applied only to primary symptoms and had collected his materia medica by selecting what he thought were the primary symptoms caused by each remedy. A therapy in which a remedy is chosen by the similarity between (what the homeopath thinks are) the secondary symptoms of the patient with the (primary) ones described in the treatises of Materia Medica is not homeopathy and does not obey the law of the similes.

1: The cornerstone of the new anatomy, as developed during the Renaissance is the De humani corporis fabrica by Andrea Vesalio (published 1540); that of physiology the Exercitatio anatomica de motu cordis et sanguinis in animalibus by William Harvey (published 1628).

2: The father of modern pathology and morbid anatomy is Giovanni Battista Morgagni, who in 1761, aged eigthy, published the De sedibus et causis morborum per anatomen indagatis.

3: An example is given by Ambroise Pare', military surgeon in the French army, who stopped using the unhealthy and damaging medication of his times and limited himself to cleaning and bandaging war wounds when he realized that such a mild approach caused better results. Pare's motto, 'I medicated my patient and God healed him', was a clear acknowledgement of the futility of many of the then available therapies.

4: Hahel, the author of a classical Hahnemann's biography, quotes (vol. I, p.170) Hufeland professor of medicine at Berlin and editor of the Journal fur Praktischen Arzneikunde, where Hahnemann pubblished several papers.

5: The miasmatic theory of epidemics, that we find in Hippocrates, attributes the main causal role to the fact that every individual living in the affected area is exposed, independently of any other to the same disease-causing environmental factors (e.g. polluted air, dry or humid weather, etc.). The opposite theory of contagion, invoked by Tucidides to explain the V century b.C epidemics in Athens, suggests that the disease can be transmitted from an individual to another, and requires interhuman contact. Both theories may be applicable, depending on the disease considered, e.g. hypotyroidism due to lack of iodine or scurvy may be considered cases of miasmatic, non contagious but epidemic diseases, whereas flu or measles are clear examples of contagious diseases. Cholera and yellow fever, two diseases whose miasmatic or contagious nature was actively debated during Hahnemann's lifetime do not conform strictly to either hypothesis, and should be regarded as contagious epidemics due to indirect interhuman transmission: the bacillum causing cholera is released in the environment and reaches its new human hosts via polluted water, whereas the virus causing yellow fever is transmitted via an insect vector. The indirect contagion was not anticipated and caused some confusion in the scientific investigation of XVIII century, since it allows a contagious disease to be transmitted without contact between the sick and the healthy people.

6: Germs were not discovered by Hahnemann: they had been observed by microscopists at the end of the XVII century. Possibly the first researcher to describe them was the flemish Anthony van Leeuwenhooek. The role of microscopic living entities as the agents of diseases was not demonstrated until the XIX century, although it had been hypothesized by Girolamo Fracastoro in 1546.

7: cit. in Coulter, 1994, Divided Legacy, vol.I, p.276; indeed Galeno and his followers did not attribute to the symptoms other relevance than that of suggesting the diagnosis, that in turn is essential to the choice of the therapy. Hahnemann anachronistically thought that the symptoms were the entire material counterpart of the disease, and that only the perturbation of the spirit-like vital force could be found behind the symptoms. It was implicit in Hahnemann's theory, and has been made explicit by Gray (2000), that the diagnosis is irrelevant to the choice of the homeopathic therapy. It is of the greatest importance to ask whether the patient is aware that when he consults a homeopath no diagnosis is made, and whether he understands the implications of this decision, since his symptoms may be the earliest clues of a progressive disease (e.g. cancer) that left to itself or treated homeopathically may become untreatable.

8: cit. in Nuland S.B. (1988) "I figli di Ippocrate", ed. It. Mondadori, Milano, 2002.

9: Organon VI ed., par.162-168.

10: On the distinction between primary and secondary symptoms see Organon, VI ed. par. 63-67; see also Hughes 1893, A manual of pharmacodynamics, B. Jain, New Delhi, India, 2001, Lecture V.

11: R. Hahel (1922) Samuel Hahnemann. His life and work. B. Jain, New Delhi, India reprinted 2003, p.125-126.

12: A. Campbell

13: Modern research demonstrates that the symptoms induced by drugs in the healthy provers are as a general rule irrelevant to judge their therapeutical efficacy. To discuss this point one should take into account the nosology and describe separately diseases and drugs according to their classification; some examples are as follows. Infectious diseases are caused by pathogenic microorganisms and are treated with antibiotics, that kill the microorganism inside or outside the human body. The effects of antibiotics on healthy individuals have nothing to do with their therapeutical action. Diseases due to lack of essential components (e.g. vitamins) of the diet are cured by dietary supplements, that usually do not cause any symptom. Diseases due to metabolic deficits (e.g. phenylchetonuria) are best treated by removing some offending nutrient from the diet (i.e. without the use of drugs). Endocrine deficits are treated by the administration of the hormone that the patient cannot synthesize (e.g. insulin for diabetes); this would cause symptoms in the healthy prover, but they generally tend to be opposite to those of the disease.

14: The term "wisdom of the body" refers to the self-healing capacities of our organism and is used by D. Ullman.

15: Dooley T., "Beyond flat earth medicine", Timing, San Diego, CA, USA, 1995.

16: The quotation is from B. Gray, "Homeopathy, science or myth?", North Atlantic Books, Berkeley, CA, USA, 2000; the reader may find a similar concept in P. Bellavite and A. Signorini "The emerging science of homeopathy", North Atlantic Books, Berkeley, CA, USA, 2002.

17: Hughes 1893, A manual of pharmacodynamics, B. Jain, New Delhi, India, 2001, Lecture V, p.67-70

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