The single remedy means only one remedy at a time is prescribed to the patient.

This is an important concept because in order to cure effectively, the homeopath must have a knowledge of the disease in all its relations to the human body, or he is "crippled and in darkness to the whole or totality" [Kent, Lesser Writings].

This amounts to a great deal of knowledge because homoeopathy is a science based upon the Law of Similars, and the prescriber must have enough information in order to be able to derive the correct similar, as well as to exclude remedies when they are not indicated.

Knowledge required includes causes, morbid anatomy, duration and course of the disease. In addition the habits of the disease must be observed to acquire knowledge of its true nature, and to be able to understand what stage the disease is at (all non-surgical diseases are dynamic), and to predict how the disease is likely to progress.

The disease picture can therefore be very complex and it is tempting to break it down and prescribe for fragments of the disease picture using different remedies to cover different parts. However this is not seeing the whole picture, not following the Law of Similars, and is therefore unsatisfactory: the whole picture should be prescribed for with one remedy which covers the totality of symptoms.

Hahnemann states it is never necessary to give more than one remedy at a time and for this reason alone the practice is inadmissible it violates the law. He argues that simple remedies are complete in themselves in their curative action, whereas two or more in combination will have unpredictable effects because they will interact or interfere with each other.

Their effects cannot be properly evaluated as there is no way of knowing which component acted. They will have different time effects, and one may heal and the other antidote. If aggravation occurs it is unclear which remedy should be followed up which one has caused the aggravation? Similarly with amelioration.

It is really common sense not to use complex methods when simple ones work. And even if the exact simple remedy cannot be found, it is still better to use it because it will clarify the picture by throwing up new complaints. A combination would merely confuse the picture with its array of symptoms.

Also, provings are not conducted on combinations so there is not enough information about their effects. Too many vibrations are created and one would be lucky to strike a chord thereby. Indeed the cure would be worse than the problem as future treatment would involve having to unravel the equivalent of a tangled piece of string instead of a single knot.