Homeopathy is approximately two hundred and fifty years old medical system.In homeopathy,extremely small dose of original substances is used to treat diseases that produce similar symptoms of the disease.Therefore,two principles of homeopathy are the law of similars and the law of minute dose.Hahnemann proposed that similar symptoms produced by remedies occupy the space of the disease.Reaction or withdrawal effect of the remedy goes against the symptoms of the disease and thus the disease is cured.Although similar substances are used to treat diseases,some substances produce both similar and opposite symptoms of the disease.Again many substances used in minute dose previously exist in the body as large doses.The other principles of homeopathy are the law of chronic diseases and the law of vital force.Hahnemann considered psora or scabies like syphilis.Like syphilis,he considered skin symptoms as primary symptoms and chronic diseases as secondary symptoms.On the other hand,high potency homeopathic remedies do not contain any original substance to produce a reaction or withdrawal effect and'vital force'theory has been refuted in modern science.Therefore these two principles have limitations too.Hahnemann proposed that water is able to retain the memory of the original substance.Modern observers suggest that water can form nanoparticles like original substances.But there is no strong proof that nanoparticles are found in bloodstream or breast milk.To explain homeopathy these limitations should be amended.