A proving (from the German word for testing) is the method used by homeopaths to test a substance so that it can be used as a remedy. The substance is first prepared by potentisation, and then volunteers (the provers) are usually given the 30c potency (though a different one may be used on occasions) until they start to show a response. The provers are not told what the remedy is, and they are not in communication with each other, and their responses are recorded by themselves and by observers, who also do not know what the remedy is. The records of the provers' reactions are collected together as the proving of the remedy.
These responses are temporary and vary from person to person, but the total information has a pattern unique to that substance and is used as the basis of treatment. By using provers with as wide a variety of differences as possible, the maximum amount of information can be gathered, enabling the fullest understanding of the general and specific properties of the substance. Other information may be gathered from reports of poisonings and from subsequent clinical use.
Warning: Repeatedly taking any potentised remedy can lead to harmful results.
The importance of these tests was made clear by Dr Samuel Hahnemann (1755-1843), when he stated that
Therefore medicines, on which depends man’s life and death, disease and health, must be thoroughly and most carefully distinguished from one another, and for this purpose tested by careful, pure experiments on the healthy body for the purpose of ascertaining their powers and real effects, in order to obtain an accurate knowledge of them, and to enable us to avoid any mistake in their employment in diseases, for it is only by correct selection of them that the greatest of all earthly blessings, the health of the body and of the mind, can be rapidly and permanently restored. 
1. Samuel Hahnemann (trans. William Boericke), Organon of Medicine, 6th edn, manuscript completed 1841, 1st English edn 1921 (Calcutta: Roy Publishing House, repr. edn 1972), § 120 p. 187.
Why it works