Organon 6

The unprejudiced observer – well aware of the futility of transcendental speculations which can receive no confirmation from experience – be his powers of penetration ever so great, takes note of nothing in every individual disease, except the changes in the health of the body and of the mind (morbid phenomena, accidents, symptoms) which can be perceived externally by means of the senses; that is to say, he notices only the deviations from the former healthy state of the now diseased individual, which are felt by the patient himself, remarked by those around him and observed by the physician. All these perceptible signs represent the disease in its whole extent, that is, together they form the true and only conceivable portrait of the disease.*

* I know not, therefore, how it was possible for physicians at the sick-bed to allow themselves to suppose that, without most carefully attending to the symptoms and being guided by them in the treatment, they ought to seek and could discover, only in the hidden and unknown interior, what there was to be cured in the disease, arrogantly and ludicrously pretending that they could, without paying much attention to the symptoms, discover the alteration that had occurred in the invisible interior, and set it to rights with (unknown!) medicines, and that such a procedure as this could alone be called radical and rational treatment.

Is not, then, that which is cognizable by the senses in diseases through the phenomena it displays, the disease itself in the eyes of the physician, since he never can see the spiritual being that produces the disease, the vital force? nor is it necessary that he should see it, but only that he should ascertain its morbid actions, in order that he may thereby be enabled to cure the disease. What else will the old school search for in the hidden interior of the organism, as a prima causa morbi, whilst they reject as an object of cure and contemptuously despise the sensible and manifest representation of the disease, the symptoms, that so plainly address themselves to us? What else do they wish to cure in disease but these?