The Similarity Theorem – Similia similibus curentur

Similia similibus curentur – English: Like cures like (Latin: Similis = similar) – Simila^[1] : the similar

The principle of similars was first formulated for drug therapy in 1796 by S. Hahnemann as the foundation of homeopathy. In general, the principle describes a stimulus-regulatory concept based on the similarity between the disorder and therapeutic stimuli. For the selection of homeopathic remedies, the diagnostic criteria are based on empirically determined (patho-)physiological reactions to the remedies used. These should correspond as closely as possible to the symptoms of the individual case in order to achieve a curative response or, in advanced cases of illness, a palliative effect.

It is essential that this is a systematic concept for prescribing remedies, which, as a minimal algorithm, produces targeted therapeutic effects. A further advantage lies in its interdisciplinary applicability.

Over the course of 225 years, there have been numerous discussions as to whether this working hypothesis established by Hahnemann is a law of nature, a principle, a rule or a concept. To clarify the debate, the following interpretation of the terminology is based on a conceptual analysis.

Law of nature

This refers to a precise, (mathematically) formulated statement regarding the course of natural phenomena, which can be applied universally, as it describes a pattern in nature (within a defined scope of validity) independently of time and place and explains it in its context.

As hypotheses formulated in the sciences are usually provisional and subject to change depending on the state of research and knowledge, there are only a few laws of nature with such overarching validity (universal statements), such as the law of conservation of energy, the three laws of thermodynamics^[2] or the law of gravity^[3] .

(See also Encyclopaedia of Biology – Laws of Nature, accessed on 11 May 2026 at https://www.spektrum.de/lexikon/biologie/naturgesetze/45456)

Principle

A principle describes a fundamental rule that determines a way of thinking, general approach and course of action. For this reason, principles are formulated in abstract terms. They serve as a guide, particularly in complex situations.

Principles determine the orientation of ways of thinking by providing structuring basic assumptions that influence how information is perceived, processed and evaluated. Depending on the field, a distinction can be made between scientific, philosophical, legal, technical, organisational or even moral principles.

In science and education, principles such as impartiality and objectivity, empiricism and reproducibility, consistency and coherence, logical consistency and verifiability are regarded as fundamental, as are ethical standards and integrity (see also Ethics in Practice).

Significance for medicine

The Hippocratic Oath and its further development in the Geneva Declaration^[4] also define the ethical principles of medicine.

The principles of empirical research in medicine are currently determined by study designs employing appropriate mathematical analytical tools from biostatistics. These are based on scientific principles and primarily utilise the tools of empirical analysis.

Rule

Rules describe guiding principles that determine procedures established by agreement. The term ‘regula’, derived from Latin, means standard, guide or guideline. In knowledge-based systems, rules are based on premises that lead to conclusions (logical conclusions) and a logical course of action.

A collection of rules is referred to as a set of rules, which consequently sets standards. They may relate to communication, behaviour and, more generally, to how one deals with something.

Practical experience shows that rules are derived not only from laws and principles, but also emerge from general insights or arise as agreements based on everyday experiences. The latter is encapsulated by the well-known saying: ‘Rules regulate’, provided that the processes in question are recognised as sensible and practised by the majority of users.

Significance for medicine

In medical practice, rules are defined as guidelines that are constantly reviewed and adapted as our understanding and knowledge grow. Guidelines are recommendations that describe the appropriate course of action. They are intended to assist in diagnosis and treatment by helping to assess and determine the most appropriate procedure for a specific individual situation.

Concept

The Latin term concipere has a broad meaning which, depending on the context, includes comprehending, grasping, imagining, summarising, composing, perceiving, or even taking in, becoming pregnant (conception).

Philosophically, a concept is an abstract and general idea, a stable notion that is as objectifiable as possible stable notion and thus a structuring abstraction that classifies and determines all the characteristics of logical examination and action. The process of concept development is referred to as conceptualisation.

Conceptualisation follows the purpose of transforming thinking—both in general and in specific instances—about something into something concrete, making it comprehensible and applicable.

Concepts thus form the link between abstract thought and concrete practice by developing and providing a systematic framework through which purposeful actions in the world can be shaped.

Concepts are always representations of reality. Conceptualisation depends on the premises of the style of thinking applied. Across the centuries, the various philosophical schools of thought have agreed that it is not possible to conceptualise all knowledge in a universally valid way. Rather, it depends on the perspective of the style of thinking and the premises set.

From a utilitarian standpoint, the observable and verifiable usefulness constitutes the defining feature of stable concepts.

Significance for medicine

Both historically and in the present day, concepts form the basis of our understanding of disease and health and thus shape the specific approach to diagnosis and treatment. They consistently follow the prevailing paradigms of understanding and action. Since the shift from purely empirical medicine to a scientifically defined approach, as developed in the 19th and 20th centuries (see also Concepts of Health and Disease), modern medicine has focused primarily on scientific concepts. Expanding this to include a broad humanistic approach is a central task for the 21st century.

Analysis and evaluation

After analysing all the foundational aspects of homeopathy in both theory and practice, including its historical development since 1805, it appears—given the current state of knowledge—appropriate to define the homeopathic principle similia similibus curentur as a principle that prestructures a mode of thought from which Samuel Hahnemann developed a practical application concept through his empirical research (see also Premises and Self-understanding - The Principle of Similars in Medicine).”

The text in the Organon of Medicine documents the practical application of the concept with its essential rules of application in the sense of guidelines.

Regardless of the further development of knowledge in the eras following Hahnemann, the concept of similiars has remained a stringent primary premise of homeopathy’s self-understanding right up to the present day. In summary, it can be stated:

From an epistemological standpoint, the similarity theorem similia similibus curentur is a theoretical principle, while in concrete practice it takes the form of an application concept

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^[1] In ‘classical homeopathic jargon’, the term ‘simile’ is used to refer to the prescribed single remedy, whilst ‘similimum’ refers to the most suitable, most similar remedy with the demonstrably best effect.

^[2] (a) The energy of a closed system is constant, (b) thermal energy cannot be converted arbitrarily into other forms of energy, and (c) absolute zero is unattainable.

^[3] Every point of mass attracts every other point of mass in a space with a force that is directly proportional to the product of their masses and inversely proportional to the square of their distance; therefore, F = G * (m₁ * m₂) / r², where F is the gravitational force between the two bodies, G is the gravitational constant (G) 6.674 * 10⁻¹¹ N m²/kg², and m₁ and m₂ the masses of the two bodies, as well as the distance between the two bodies (r).

^[4] Geneva Declaration of the World Medical Association on the Physician’s Oath, adopted in 1948, current version: https://www.bundesaerztekammer.de/fileadmin/user_upload/BAEK/Themen/Internationales/Bundesaerztekammer_Deklaration_von_Genf_04.pdf

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Authors: glt | Rev.: gbh, mnr, sfm, smi | Ed.: pz | Last modified May 14, 2026