Certain professors of the Ayurveda hold that a medicinal drug or substance is pre-eminently the most important matter with which the science of medicine is concerned. First because, a drug, as a substance, has a definite and continuous existence, which its attributes (such as, taste, etc.,) do not possess. As for example the tastes, etc., which characterise a fruit in its unripe stage, are not perceived in its ripe or matured condition. Secondly because, a drug is real (Nitya) and invariable, whereas its attributes are but transitory and accidental at the best. As for instance the real character of a drug cannot be destroyed whether it be powdered or pasted. Thirdly because, a drug or a substance never can lose its own generic character. As for example, a drug possessed of attributes peculiar to the fundamental matter, earth, can never be transformed into one of watery attributes - a truth which does not hold good of its attributes. Fourthly because, a drug or a substance is an object of all the five senses of a man, whereas its attributes of tastes, etc.
are respectively accommodated to the faculty of special sense organs. Fifthly because, a drug or a substance is the receptacle of the attributes of taste, etc., while the latter are the things contained. Sixthly because, a dictum of medicine can be commenced with the name of a drug or substance. As for example, it is quite natural to say that the drugs such as Vidari Gandha,etc, should be pressed and boiled. But it sounds preposterous to utter that the sweet taste should be pulverised and boiled. Seventhly because, the greater importance of a drug or substance has been laid down in the Shastras of medicines inasmuch as medical recipes have been described by the names of their component ingredients such as Matulunga, Agnimantha, etc., and not described as the tastes of Matulunga, Agnimantha etc. Eighthly because, the attributes of tastes, etc., depend upon the drugs and substances (of which they are the attributes) for their progressive maturity. As for example, the taste of a drug or substance varies with its growth and is different in its raw (immature) and ripe (mature) conditions. (Hence a drug is more important than its attributes of taste, etc.) Ninthly because, a drug may prove curative through the efficacy of one of its component parts or principles as in the case of Mahavriksha, the milky exudations of which are possessed of therapeutical virtues, which cannot be said of its taste.
Hence a drug or a substance (Dravyam) is the most important factor (which the science of medicine has got to deal with). A substance or drug necessarily implies action and attributes with which it is intimately connected and of which it is the primary cause, or to put it more explicitly, these attributes have an inseparable inherence in and are intimately associated with the substance by way of cause and effect (Samavayi-Karanam).
Others, on the contrary, who do not endorse the above opinion, accord the highest importance to the attribute of taste (Rasa) of a drug or substance. Firstly because, it is so laid down in the Agamas (Vedas), which include the science of medicine (Ayurveda Shastram) as well, and inasmuch as such statements as "Food is primarily contingent on its tastes and on food depends life" occur therein. Secondly because, the essential importance of taste may be inferred from such injunctions or instructions of the professors of medicine as, "sweet, acid and saline tastes soothe or pacify the deranged bodily Vayu." Thirdly because, a drug or a substance is named after the nature of its taste, as a sweet drug, a saline sub-tance, etc. Fourthly because, its primary importance is based on the inspired utterances of the holy sages (Rishis) which form the sacred hymns and verses of the Vedas, and such passages as "sweets to be collected for the purposes of a religious sacrifice," etc., are to be found in them, Hence taste is the most important factor in the science of medicine and forms the primary attribute of a medicinal drug. But, later on, we shall have occasion to speak of that.
Certain authorities however, (who reject the two aforesaid theories), hold the potency (Viryam) of a drug to be the most important factor in medicine inasmuch as its therapeutic action, whether purgative, emetic, or both, or cathartic, or pacifying, or astringent, appetising, pressing (drawing to a definite head) or liquefacient, or constructive, tonic (vitalising) or aphrodisiac, or inflammatory, absorbing, caustic, or bursting, or intoxicating, soporific, killing or antitoxic, depends upon its potency. The potency of a drug is either cooling or heat-making owing to the twofold (hot and cool) nature of the temperament of the world. According to several authorities the potency of a medicinal drug may be classed as either hot or cool, emollient or dry, expansive or slimy, mild or keen, so as to embrace the eight different attributes in all. These potencies of medicinal drugs serve their respective functions by overpowering their (drugs') tastes with their specific strength (intensity) and virtues. As for example the decoction of the roots belonging to the group of the Maha-Panchamulam, though possessed of an astringent taste which is subsequently transformed into a bitter one, acquires the virtue of pacifying the deranged Vayu out of its heat-making potency. Similarly, the pulse known as Kulattha though possessed of an astringent taste, and onion though endued with a pungent one, respectively soothe the same deranged humour of the body through the oleaginous character of their potencies. On the other hand, the expressed juice of sugar-cane, though possessed of a sweet taste, tends to augment or aggravate the deranged Vayu owing to its cooling potency. The drug Pippali, though a pungent substance in itself, proves soothing to the deranged Pittam, owing to its mild and cooling potency. Similarly, an Amalakam fruit, though acid in taste, and Saindhava, though saline, respectively tend to pacify the deranged Pittam. The drug Kakamachi, though of a bitter taste, and fish, though sweet, respectively aggravate the Pittam, owing to their thermogenetic potency. Similarly, Mulakam (Radish), though pungent, increases the Kapham of the body, on account of its emollient potency; and Kapittham, though acid, soothes; and honey, though sweet, tends to pacify the deranged Kapham owing to the dry character of its potency. The aforesaid instances have been cited by way of illustration.