The proper translation and understanding of the key element of the Ayurvedic tradition, the tridosha, remains at the heart of making Ayurveda accessible to those who did not grow up with and assiduously study this field. As to understanding the tridosha system, in the introduction to the Indian Materia Medica, this is offered:
The doshas-vayu, pitta, and kapha-constitute the tripod on which Ayurveda stands. To understand their theory perfectly and correctly is by itself a long and arduous study. The subject being a very complicated one, it cannot be explained within a few pages. Also, it has been defined by different experts in different ways, but the basic principles to which they all point to are the same.
Dr. Nadkarni suggests that the tridosha system actually represents two forms of doshas:
1. An invisible or essential form, which mainly guides the physiological processes pertaining to them naturally.
2. A crude or visible form, the products (as secretions or excretions) of those processes induced by these essential forms.
The relation between the two forms is very close, so that the derangement of the essential form of one principle gives rise at once to increased or morbid secretions and excretions of that principle.
In other words, the Ayurvedic system describes an influence-one or more of vayu, pitta, and kapha-and there are the material results of those influences, which might be referred to as humors, secretions, and excretions, but which have been given the same names.
These two forms-influence and manifestation-are easily confused, and it is seen in the Ayurvedic medical literature that the flow of thought back and forth between these two aspects leads one to easily forget which is the focus of concern. Further, each of these three influences is not solely pathological, despite the frequent reference to their role in pathology. They are pathological when there is an excess or deficiency or some other type of deviation from normal (most often an agitation); otherwise, they are essential to life. In fact, in the traditional Ayurvedic system, when vayu, kapha, and pitta are in their normal measure they are described as supporters of the body; but they are considered doshas (literally: faults) if they are producing imbalance. So it is that one can become disoriented by considering a fundamental entity, defined by a single word such as vayu, as being both essential and pathological, a causative factor and a result, a symbol, an influence, and a manifestation.
Pitta, kapha, and vata (vayu) have been translated as bile, phlegm, and wind, respectively, based on translations that arose out of the ancient Greek system. These terms are poor representatives of the underlying meaning, however. One can understand the terminology conundrum by reading the description of vayu in the Charaka Samhita. On the one hand, vayu is described this way:
When moving in the world in an excited state, without doubt, vayu achieves the following functions: It breaks the summit of mountains. It uproots trees. It agitates seas. It swells the waters of lakes causing them to rise upwards. It causes the currents of rivers to run in opposite directions. It makes the earth tremble. It urges the clouds. It causes frost, thunder, dust, sand, fish, frogs, snakes, ashes, blood, stones, and lightning to fall down on the earth. It causes excess of virtues, absence of virtues, and contrariety of virtues in respect of the six seasons. It causes failure of crops. It produces disease and plagues. It destroys many objects.
A large part of this description sounds like wind as we all know it, at least as it occurs in hurricanes and tornadoes (it is only so destructive in the "excited state"). A portion sounds like infectious agents (pests, pathogenic fungi, viruses, etc.) that cause crop failures, diseases, and plagues.
When describing vayu as an aspect of the human body, it takes on a different form. Here is the Charaka Samhita presentation of its favorable side, that is, when not "excited" (the parenthetical statements being clarifications included by the translators):
The wind upholds the constituents of the body (such as blood, flesh, marrow, fat, etc.) and their courses through the body. It exists in the five-fold form of prana, udana, samana, vyana and apana. It is the urging cause of movements of diverse kinds. It restrains the mind (from all undesirable objects) and concentrates it (on objects that are desirable). It causes all the (ten) senses (of knowledge and action) to perform their functions. It bears all the objects of the senses (after contact with the senses) to the mind. It holds together all the elements of the body. It assists the cohesion of the particles of the body. It causes speech. It is the prime cause of touch and sound, and the root of scent and touch. It is the origin of joy and cheerfulness. It excites the heat of fire. It dries up all faults. It throws out all impurities. It pierces through all the ducts of the body, gross and fine. It gives form to the embryo in the womb. It furnishes evidence of the existence of life. The wind, when unexcited, achieves all these functions.
The idea that wind encompasses all the functions of the central nervous system or that its main function is to provide for any movements within or of the body, as many modern writers suggest in their depictions, doesn't seem to fit all that well with the above description. The Charaka Samhita continues:
When excited within the body, vayu pains the body with diverse afflictions. It destroys and injures strength, complexion, happiness, and duration of life. It agitates the mind. It injures all the senses. It kills the embryo and causes miscarriage. It maims the embryo (by suspending the development of particular parts). It holds the fetus longer than usual. It causes fear, grief, stupefaction, cheerlessness, and delusions. It destroys life.
Here, the agitation of mind, injury to senses, and the development of various mental states and delusions that result from agitated wind all seem consistent with a role of the central nervous system. Then, additionally, pathological vayu has adverse effects on pregnancy.
The translation term for vayu as wind is probably as good as one can manage to capture this diverse traditional concept in one word. Likewise, the term feng in traditional Chinese medicine, translated as wind, is equally problematic; it also has some connections with the central nervous system (wind diseases often involve involuntary muscular conditions and abnormal sensory conditions, which are related to central nervous system activity), perhaps more so than in the Indian system. Vayu, unlike pitta and kapha, has its own chapter in the Charaka Samhita; in fact, it has two full chapters. It is the condition that requires the most explanation, and did so even in ancient times.
The description of pitta as bile has some similar problems. According to the Greek tradition, there were three humors in the body: blood, phlegm, and bile (the latter could be subdivided into two forms: yellow and black). The term bile was simply carried over to explain the term that arose in the Indian system. In both those traditional systems, it was associated with burning sensation and feverish condition, though that is nearly the full extent of the connection. Reference to pitta in terms of heat or "fire" is probably more appropriate, but in the Ayurvedic thinking, pitta is also liquid (oily), like bile, so it differs from the "dry" connotation of something that is burning. In the Ayurvedic system, there is a manifestation of pitta, called agni, which is often translated as digestive fire, and we understand that to be the highly active aspect of transforming food into its useful components, as a cooking fire transforms raw food into edible cooked food. But, the digestive juices, including actual bile, are fluid in nature.
The term phlegm fits kapha sufficiently to be usable, though it remains far from ideal. In the Ayurvedic system, the qualities of cold, damp, and thickness go together in this concept. We might think of the common cold, with its chills and excess production of mucus (phlegm). But, other thickened fluids of the body (including normal ones that are lubricant and protective) are also associated with kapha. So long as one understands that the translation terms are applicable to broad traditional concepts rather than limited modern definitions, one should be able to make use of them in communicating general ideas about the use of Ayurvedic medicine.
To sum up tridosha in a few words, one of the leading Western authorities on Ayurveda, Robert Svoboda, in his book Ayurveda: Life, Health and Longevity, has said this:
The three doshas enable the spiritual and mental planes of existence to express themselves through the physical body. Vata is in charge of all motion in the body and mind. Everything that moves, from a molecule to a thought, moves because of vata, and every motion of any kind influences every other motion....Pitta is in charge of all transformation in the organism. Digestion of food by the gut, of light by the eyes, and of sensory data by the brain are examples of pitta's activities. Kapha is the stabilizing influence in the living being. It lubricates, maintains and contains, and its various activities, like those of vata and pitta, are interrelated.