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.
Hahnemann calls especial attention to the "more striking, singular and uncommon, peculiar signs and symptoms of a case of disease" which are chiefly to be kept in view. These symptoms of themselves may be of no special value, but become valuable or characteristic by their conditions of aggravation or amelioration, their concomitants or locality. Transient odd and peculiar symptoms are however not so important as such as affect the patient's general condition, hence the modalities, conditions of aggravation and amelioration effects of heat, cold, weather, position, times of day, etc , are most important. The modalities of a drug are the pathognomonic symptoms of the Materia Medica.
Mental symptoms of drugs are most important, and are a very pronounced feature in the pathogenesis of certain drugs. Notice the mental state of the patient particularly; does he suffer patiently or otherwise. They are also of great importance prognostically; improvement in the mental condition often precedes bodily and general improvement.