This section is from the book "A Compend Of The Principles Of Homoeopathy", by William Boericke. Also available from Amazon: A Compend of the Principles of Homoeopathy as Taught by Hahnemann.
Modalities are conditions influencing or modifying drug action. They are the phenomena of time, place, circumstances on which the development and appearance of the symptoms depend. Every drug has its own mode of action, manifests itself in a way peculiar to itself, distinguishing it from every other. It acts best under certain conditions, in certain bodily and mental constitutions, which present, therefore, the most favorable ground and environment for the full and free manifestation of the drug's individuality. Just as a plant thrives best in certain conditions of soil, climate, elevation, etc. - needs, in short, for its perfect development, a suitable environment, - so a drug must be similarly situated to enable it to express itself clearly and fully. It is of the greatest importance in drug proving, as well as in prescribing homoeopathically, to note the peculiar method in which a drug invades the animal economy, its aggravations and ameliorations, the times of the day, and conditions of the weather, when the action is most pronounced. For instance, the marked increase of pain on motion of Bryonia, the relief of headache by wrapping head up warmly of Silica, the marked preference of the left side of the body of Lachesis, the aggravation of all the symptoms from 4 to 8 p. m. of Lycopodium, the relief by heat of Arsenic, the aggravation of damp weather of Dulcamara, are characteristic conditions of great value, clearly expressing the peculiar genius of these drugs and are paramount in estimating their place in the symptomatology. But, while they hold this important place, they must not be studied independently of the whole of a drug's action, for this is needed for their interpretation. It is a fact that the study of characteristics alone leads quickly to practical results, but also to permanent mediocrity in knowledge of drug action.
Boeninghausen's method of interpreting symptomatology consists essentially in the selection from the symptoms of the patient, and from those of the drug, of their elements, rather than try to obtain the complete symptom, which latter consists of a seat or location, a sensation and a modality; but, in the present incomplete state of our Materia Medica, most of the symptoms are fragmentary, and but few are complete in the above sense. By the use of Boeninghausen's method, these fragmentary symptoms are supplemented by clinical observation of the curative effects. A remedy is selected for a case that is found to possess in its symptomatology marked action (1) in a certain location; (2) to correspond with sensation, and (3) possess the same modality; without necessarily having in the proving produced the very symptom resulting from the combination. It is to be inferred that a full proving would have it, however. For instance, a patient with a bearing pain in the left hip, relieved by motion, greatly worse in the afternoon, would receive Lycopodium, not because Lycopodium has so far produced in the healthy such a symptom, but because, from the study of its symptoms as recorded in the Materia Medica, we do find that it affects the left hip prominently (locality); that its pains, in various parts of the body, are "tearing" (sensation); and that its general symptoms are relieved by motion and aggravated in the afternoon (modality). The only justification for such analysis and synthesis of symptoms is the imperfection and limitation of our provings and especially the success following the application of the newly constructed symptom, out of these elements, in removing similar symptoms in the patient, hence in curing, and the reasonableness of the presumption that future, complete provings will develop the missing links of the complete symptom of the drug. It is in entire harmony with the fact that every genuine symptom has these three factors - locality, sensation, and modality - these, when combined, constitute a perfect symptom. It is not usual to get these, in any one symptom, from any one prover, but they may be found scattered through the various provings; hence the legitimacy of Boeninghausen's method.
T. F. Allen's paper before the World's Medical Congress at Chicago, 1893, entitled, "The Selection of the Homoeopathic Remedy, especially in regard to Boeninghausen's Method," published, with discussions, in North American Journal of Homoeopathy, August, 1893.
For further practical illustration of the use of Boeninghausen's method see an instructive, analytical report of a case of "Progressive Muscular Atrophy Cured with Phosphorus," by T. F. Alien, reported in Hahnemannian Advocate, July 15, 1896.
For further study, consult.
"Organon," §§ 153, 164, 165, 178.
Also, the preface to Hering's "Guiding Symptoms," Vol. I.
"Hirschel's Rules and Examples for the Study of Pharmacodynamics," Thos. H. Hayle.