Law of Similia

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Law of similia is one of the cardinal principles of homoeopathy.

‘Similia similibus curenter’ is the Latin expression of the words ‘Let like be treated by likes’. Hahneman arrived at this therapeutic formula from the already existing law of nature ‘similia similibus curantar’ which means ‘like cures likes’. Hahnemann reached this law through inductive reasoning. He established the fact that this law is not of occasional occurance but of universal adaptability as a general law of permanent cure, for all physical and mental ailments of mankind.

The recognition of this law existed even before Hahnemann. Paracelus, Hippocrates, and ancient ayurvedic texts have on occasions mentioned this law. But it was Hahnemann who recognized the universality of this law and made it the basis of a complete system of medicine. According to this system, the choice of the medicine is fundamentally based on the principle that the medicine must have the capability of producing most similar symptoms of the disease to be cured in healthy persons.

In aphorism 26 of 'Organon of Medicine', Hahnemann states this law: "A weaker dynamic affection is permanently extinguished in the living organism by a stronger one, if the latter (whilst differing in kind) is very similar to the former in its manifestations."


A rude testimony of a barbarous age to the truth of what we know to be one true law in medicine. This represents that the outward and visible form of a drug as expressed by its taste , smell , color and appearance will give an indication to its therapeutic use . The plant mandrake resembles a small child so it can be given for sterility . Euphrasia resembles the eye so it can be given for eye affections .

Discovery of Similia:

In 1790, Hahnemann took to the task of translating Cullen’s M.M. and this turned to be the first milestone in the road of development, of the new method of treatment. In question of the medicinal effects of Peruvian bark Cullen defended the old opinion of efficacy of this remedy through its astringent property and tonic effect on the stomach. Hahnemann attacked this opinion vigorously in his notes (Vol II ,pg 108): “By combining the strongest bitters and the strongest astringents we can obtain a compound which in small doses, possesses much more of both these properties than the bark, and yet in all eternity no fever specific can be made from such a compound”. Thus Hahnemann on translating Cullen’s M.M. became indignant over the affect theoretical explanations of the antipyretic power of cinchona bark and therefore resolved to ascertain by the natural method of experience and thereby made the first experiment upon himself .He took an ounce of cinchona bark and was surprised to see that the symptoms evolved were similar to marshy fever .

Hahnemann here sensed a law that thought him to recognize that the effect a substance has on healthy organism is its curative power. Hahnemann then conducted experiments upon his family members and followers and thus confirmed his conclusions . Thus from the particulars he was able to reach a general conclusion using the inductive method of reasoning . Hahnemann’s enquiry as to under what circumstance the drug is curative lead to a new way of proving drugs upon the healthy and also to the conclusion that it is not the astringent property of china but its ability to produce similar symptoms that gave it the curative power. Hahnemann enunciated this principle in 1796 in his essay On the new principles for ascertaining the curative power of drugs and some examination of its previous principles .And this lead to the birth of a new system of medicine viz homoeopathy.

Scientificity of similia
As the law of similia confirms to all requirements in the derivation of a law we can pronounce it as a scientific law . Any law is a scientific law when it satisfies the following requisites .
1) Collection of data
2) Interpretation
3) Formation of hypothesis
4) Verification as a thesis

Collection of data
Exact observation led Hahneman to see that law of similars was dimly perceived by various physicians before his time like Hippocrates , Nicander , Xenocrates , Celsus, Galen , Valentine , Paracelsus etc . He got further proof in the records of provings and accidental cures . Many contemporaries also testified to the authencity of this principle. Hahnemann experimented upon himself , his family members and his followers .


Through the accumulation of more data, Hahnemann was able to reduce the possibility of error and correctly interpret the observed facts. On the basis of observed data and experimentation , he was able to interpret. Guided by the inductive method of logic that the law of similars is a general law derived from various individual facts.

Formation of hypothesis

A rational explanation that disease are cured by medicines that have the power to excite a similar affections was put forward . This lead to the formation of a hypothesis which needed further verification to become a thesis.

This general law was applied to each and every particular case of disease and the results obtained were studied. Thus Hahnemann through inductive and deductive logic laid the foundation of a true scientific system. By the application of this general law many diseases even new and previously unknown were successfully treated. Many observed and recorded facts of clinical trials over the centuries abounding the literature of homoeopathy also testifies to the validity of this law.

Thus scientificity of similia was constructed through inductive logic and clinically verified through deductive method of logic. Law of similia ranks equal to the universal law of natural sciences.
In physics the phenomenon of sun is related to phenomenon of earth by law of attraction . In chemistry , properties of potassium is related to properties of sodium through law of chemical affinity and definite proportion . Similarly drug phenomenon is related to disease phenomenon through law of similars .

It not only establishes a relationship between proved drug and known disease phenomenon but also between unexplored medical wealth and undeveloped medical requirements of the sick i.e. new and unknown diseases can be successfully treated by collecting its totality of symptoms.