In short: Similia similibus curentur, "let likes be cured by likes", also written similia similibus curantur, is the law of similars, the founding principle of homeopathy: a substance that produces a set of symptoms in a healthy person is the one chosen to treat a similar set of symptoms in a sick person. Hahnemann reached it through his 1790 self-experiment with cinchona bark, published it in 1796 and stated it as a law in §26 of the Organon; provings, the totality of symptoms, the single remedy and the minimum dose are the working rules he derived from it. It is a doctrine, summarised in English as "like cures like", not an established therapeutic law.
This guide is written for practitioners and students who need the phrase, its two spellings, its source passages and the principles that hang from it, stated precisely enough to cite. It is a historical account of a doctrine, not evidence of clinical effectiveness and not self-treatment advice.
What "similia similibus curentur" means, and the curentur / curantur question
Word by word: similia, like things; similibus, by like things; curentur, let them be cured. The phrase is an instruction to the physician, and curentur is Hahnemann's own wording. In the introduction to the Organon he describes the healing art he set out to found as one that restores health "by means of smallest doses of few simple medicines carefully selected according to their proved effects, by the only therapeutic law conformable to nature: similia similibus curentur".
Curantur is the indicative: likes are cured by likes, a statement rather than an instruction. It is the form some reference works index; Italian Wikipedia, citing the Enciclopedia Treccani, heads its entry "Similia similibus curantur" and notes curentur as the less frequent spelling (source: it.wikipedia.org, 20 September 2026). The two forms name the same principle; write curentur when you cite Hahnemann.
Each language's literature has its own term. In German the principle is the Ähnlichkeitsprinzip or Simile-Prinzip, sometimes Ähnlichkeitsgesetz or Ähnlichkeitsregel; in Spanish the ley de los semejantes or principio de similitud; in Italian the principio di similitudine; in French the loi de similitude of homeopathy. In English it is the law of similars or, colloquially, "like cures like".
Where Hahnemann stated it: 1790, 1796 and the Organon
1790, the cinchona trial. In 1790, translating William Cullen's Materia Medica into German, Hahnemann took Peruvian bark himself while healthy. His own account is a footnote in the China chapter of the Materia Medica Pura (vol. iii, second edition, 1825), readable in full on Similia's free reader for Hahnemann's China: "As long ago as the year 1790 … I made the first pure trial with cinchona bark upon myself, in reference to its power of exciting intermittent fever. With this first trial broke upon me the dawn that has since brightened into the most brilliant day of the medical art; that it is only in virtue of their power to make the healthy human being ill that medicines can cure morbid states". The translation is R. E. Dudgeon's, annotated by Richard Hughes (1880–1881).
1796, the essay. Six years later Hahnemann published the principle in a German medical journal as the Essay on a New Principle for Ascertaining the Curative Powers of Drugs (Versuch über ein neues Prinzip zur Auffindung der Heilkräfte der Arzneisubstanzen); 1796 is conventionally taken as the birth of homeopathy.
The Organon, §§22–29. The Organon of the Rational Art of Healing (1810) turned the principle into a system; the sixth edition, completed in 1842, published in 1921 and translated into English by William Boericke in 1922, supplies the aphorism numbers cited here. The argument runs in sequence:
- §§22–23. Nothing is observable in a disease except its symptoms, and nothing curative in a medicine except its tendency to produce symptoms in the healthy and remove them in the sick; the medicine sought must therefore have "the greatest tendency to produce similar or opposite symptoms", and experience decides against opposites, which relieve briefly and then return the symptom "with increased intensity".
- §§24–25. There remains only the homeopathic mode, which seeks, for the totality of the symptoms, the medicine that produces "an artificial morbid state most similar" to the case; pure experience, "the sole and infallible oracle of the healing art", confirms it.
- §26, the law itself. "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."
- §§27–29. The curative power of a medicine therefore lies in symptoms "similar to the disease but superior to it in strength". Hahnemann says the fact is established by observation, attaches little importance to explaining it, and then offers in §29 the explanation he thought most probable: the stronger artificial disease takes the place of the natural one and, being of short duration, soon spends itself.
For the editions, the structure of the 291 aphorisms and how to study the book, use the Organon guide; this page stays on the one principle.
Similars, contraries and isopathy: three ways to choose a medicine
Contraria contrariis curantur
"Contraries are cured by contraries" is the rule of opposites that Hahnemann attributes, in §56, to Galen's teaching and to seventeen centuries of practice after him. He calls it the antipathic, enantiopathic or palliative method: for a single troublesome symptom, give a medicine known to produce the opposite. His examples in §57 and §59 are still the ones quoted: opium for pain, diarrhoea and sleeplessness, because its primary action benumbs, constipates and stupefies; coffee for daytime sleepiness, because its primary action enlivens. His objection, worked through in §§58–62, is that the relief is transient and the symptom returns stronger once the drug's primary action has passed: the method treats one symptom rather than the totality, and it palliates before it aggravates.
Aequalia aequalibus: isopathy
Isopathy gives the very substance, or the very disease product, that caused the complaint: the same cures the same. Hahnemann rejected it in a footnote to §56 of the sixth edition: to attempt a cure "by means of the very same morbific potency (per Idem) contradicts all normal human understanding and hence all experience", and where it appears to work, he argues, the potentised material is altered and the cure is effected "only by opposing a simillimum to a simillimum". Similar, not identical, is the whole point of the law; a nosode given on the similarity of the patient's symptoms is used homeopathically, given for the disease it came from, isopathically.
Before Hahnemann
Hahnemann did not claim the idea was new, only the system. In the Organon's introduction he lists physicians who "vaguely surmised" it, from a work attributed to Hippocrates through Boulduc, Detharding, Bertholon, Thoury, von Stoerk and a physician named Stahl, described by Hahnemann as a Danish army physician, who wrote that diseases "will yield to, and be cured by, remedies that produce a similar affection (similia similibus)". He cites them not as proof, he says, but to avoid the charge of having suppressed them. A precedent for the idea is not a system built on it.
The principles that follow from the law of similars
The law of similars is the axiom; the remaining principles of homeopathy are the working rules Hahnemann derived from it, and classical authors number them differently. Adolph Lippe reduced them to three in "Our Three Fundamental Principles": the law of the similars, the single remedy and the optimal dose, "an essential trine, an inseparable unit". The list below adds provings and the totality of symptoms, which Lippe treats as the interpretation of the first principle, and the vital force, the doctrine behind all of them.
| Principle | Sixth-edition aphorisms | What it commits you to | Where it shows up at the desk |
|---|---|---|---|
| Law of similars | §§22–29 | The medicine whose proving picture is most similar to the case | Every remedy comparison |
| Provings on the healthy | §§105–145 | Medicines are learned from their effects on healthy people | The materia medica |
| Totality of symptoms | §§7, 18, 153 | The whole characteristic picture, not the diagnosis, guides the choice | Case taking and rubric weighting |
| Single remedy | §273 | One simple medicine at a time | The prescription |
| Minimum dose | §§275–279 | The smallest dose that acts | Potency and repetition |
| Vital force | §§9–12 | Disease is a derangement of the dynamis, known only through symptoms | The rationale, not a tool |
Provings (§§105–145)
The similar has to come from somewhere, and Hahnemann's answer is §108: "administer the several medicines experimentally, in moderate doses, to healthy persons", because medicines given to the sick show "little or nothing precise" of their true effects (§107). The Materia Medica Pura (1811–1821) is the record of his own provings; at the desk this principle is the materia medica, the remedy's side of the comparison.
Totality of symptoms and the simillimum (§§7, 18, 153)
§7 makes the totality of the symptoms "the only thing the physician has to take note of in every case of disease", and §18 calls it "the sole indication, the sole guide to direct us in the choice of a remedy". §153 says which symptoms weigh most: the "more striking, singular, uncommon and peculiar (characteristic) signs and symptoms", while loss of appetite, headache or restless sleep "demand but little attention", because almost every disease and almost every drug produces them.
The simillimum, also spelled similimum, is the remedy whose proving and clinical picture most closely matches that totality of characteristic symptoms; the word is Hahnemann's own, and it appears in the isopathy footnote above. At the desk this principle is repertorisation: each characteristic symptom becomes a rubric, the rubrics are crossed, and the remedies that cover them are ranked by grade and coverage; the repertorisation guide walks the sequence. Two cautions: the highest-scoring remedy is a candidate, not a prescription, and the simillimum is confirmed by reading the candidates in the materia medica; and because the comparison is between whole pictures, a keynote confirms a remedy already indicated by the totality rather than replacing it.
The single remedy (§273)
§273 of the sixth edition is categorical: "In no case under treatment is it necessary and therefore not permissible to administer to a patient more than one single, simple medicinal substance at one time." The reasoning follows from the law: a proving describes one substance, so similarity can only be judged, and the result only interpreted, for one substance. The doctrine and its opposites are the subject of the unicist homeopathy guide.
The minimum dose (§§275–279)
§275 states that the suitability of a medicine "does not depend on its accurate homoeopathic selection alone, but likewise on the proper size, or rather smallness, of the dose", because a too-large dose of a well-chosen similar acts on exactly the parts already most affected. §278 says only "pure experiment, careful observation of the sensitiveness of each patient, and accurate experience" can fix the dose, and §279 that for chronic disease a highly potentised dose "can never be prepared so small that it shall not be stronger than the natural disease". Potentisation, the trituration, dilution and succussion of §270, is his method for reaching it. This page stays at the level of doctrine; scale, level and repetition belong to the potency selection guide.
The vital force (§§9–12)
In homeopathy the vital force is Hahnemann's term for the self-regulating principle he held to maintain health and to be disturbed in illness; it is a historical doctrine within homeopathy, not an established physiological mechanism. §9 describes it in health as "the spiritual vital force (autocracy), the dynamis that animates the material body (organism)", which "rules with unbounded sway"; §11 says that in illness this force is "primarily deranged", and that the derangement "only makes itself known by the manifestation of disease in the sensations and functions", that is, by symptoms. The German word is Lebenskraft; Hahnemann also writes dynamis and, in the sixth edition, "the principle of life". The doctrine is why the totality is the only guide: for Hahnemann there was nothing else of the disease to observe.
How Kent's Lectures on Homoeopathic Philosophy reframed the principles
James Tyler Kent's Lectures on Homoeopathic Philosophy (1900) are thirty-seven lectures delivered at the Post-Graduate School of Homoeopathics in Philadelphia and, in Kent's preface, meant to be read with the Organon "in the form of a commentary". Most students meet Hahnemann's principles first in Kent's phrasing, so it matters where Kent restates and where he adds.
The vital force as simple substance. Kent's lecture on §9 recasts the dynamis as "simple substance", an immaterial substance "endowed with formative intelligence". This is Kent's metaphysics, not Hahnemann's text, and quoting it as Hahnemann's is a misattribution.
The hierarchy of symptoms. In the lectures on the value of symptoms Kent sorts every symptom into generals, common symptoms and particulars, each in three grades: "All the things that are predicated of the patient himself are things that are general; all the things that are predicated of any given organ are things in particular." The mind comes first, because a remedy acts on "the memory and understanding and will", and the generals rank above any local complaint. This hierarchy is why his repertory (1897) opens with Mind and runs through 37 chapters to Generals.
The law itself. Lecture 13 reads §26 as Hahnemann's declaration that "the phenomena of cure depend entirely upon fixed law", and Kent adds that all other apparent cures "are not cures but suppressions".
This is also the place to define repertory philosophy, a phrase students search for and seldom find explained: the set of assumptions about symptom rank and symptom form that a repertory's structure encodes. Kent's repertory embodies the hierarchy above: start from the mental and general rubrics, narrow with particulars. Boenninghausen's builds the complete symptom from location, sensation, modality and concomitant, and generalises modalities across the body rather than tying them to one part. The Kent repertory guide sets out the first structure; the Boenninghausen and Boger method guide sets out the second. Kent's Lectures on Homoeopathic Philosophy are public domain but not on Similia; his Lectures on Homoeopathic Materia Medica are, free to read.
Hering's law, miasms and the doctrines that came after
Two later doctrines are often taught beside the principles above and should be kept apart from them. Hering's observations on the direction of cure interpret what happens after the similar remedy is given; see the Hering's law guide. Hahnemann's own theory of chronic miasms, introduced in The Chronic Diseases (1828), adds a layer to chronic case analysis; see the miasms guide. Neither replaces the similarity rule: the remedy is still chosen on the totality of characteristic symptoms, and both doctrines serve to judge or refine a prescription made under the law of similars.
Why the software is called Similia
Similia takes its name from the first word of similia similibus curentur. The platform is built for the step the phrase describes, matching a patient's symptom totality to the most similar remedy, and its two halves are the two halves of that comparison: the repertory, from symptom to remedies, and the materia medica, from remedy to symptoms.
In the Free plan that is the aphorisms in action. You type the patient's characteristic symptom in their own words, and AI semantic search of the seven classical repertories returns the rubric even when the wording differs from Kent's; the remedy list that follows is the similars, ranked by grade and coverage. The 21 classic materia medica books, Hahnemann's Materia Medica Pura among them, are free to read online, so the simillimum is confirmed in the same place. Basic case management is capped at three new cases and three analyses a month. Pro adds the AI toolkit, whose case analysis can propose a similarity analysis of a full case for the practitioner to review, together with unlimited cases and analyses and the premium repertories and materia medica; AI-toolkit operations use credits. It starts with a free account, no card required.
Primary sources
Hahnemann, S., Organon of Medicine, sixth edition, Boericke's translation (1922): introduction; §§9–12, 22–29, 56–62 with the isopathy footnote, 105–145, 153, 270, 273, 275–279. Hahnemann, S., Materia Medica Pura, China, note 1, Dudgeon's translation annotated by Hughes (1880–1881), read at the link above. Kent, J. T., Lectures on Homoeopathic Philosophy (1900): preface and lectures 8, 13, 32 and 33. Lippe, A., "Our Three Fundamental Principles". The fifth edition numbers several aphorisms differently; cite the edition you read.
