Particularly important in diagnoses are the so called key symptoms, the keynotes, symptoms that do not occur with other remedies. Some authors of Materia Medicas only search for these keynotes, such as Adolph von Lippe in his Keynotes and Red Line Symptoms. The author puts beyond the red line, leading to correct diagnoses, the chains of more symptoms, in a particular characteristic combination. Another well known Materia Medica of this kind is Allen's Keynotes. The only problem with this system is the fact that not all specific cases have such keynotes.
Every homeopath rejoices on finding any keynotes.
It is necessary to study the Materia Medica, to spend a lot of time over it, and to memorise the basic characteristics of the remedy. It is essential to gain at least so much knowledge, to be able to compare one remedy with another, and particularly the real patient with the Materia Medica. No one has managed to learn the entire Materia Medica by heart, and this is not the aim. No one expects that a barrister would know all the law books by heart either. Important is to have the orientation, and to know where to look things up.