Ayurveda is deeply rooted in exhaustive theoretical foundations, which are based on observations and metaphysical reasoning. A basic understanding of these aspects is an essential prerequisite to the understanding of the functioning of the system.

        The ancient Indians believed that both the Universe and the organisms are composed of the following five basic elements, the panchamahabhoothas:

        Concept of humoural pathology is not exclusive to Ayurveda. It is one of the very ancient concepts in medicine finding place Ayurveda, Siddha, Tibetan medicine. Unani and the medical systems of China, Europe, Latin America and Philippines. The humoral theory of Ayurveda is a comprehensive approach to the three major branches of medcine, physiology, pathology and treatment. A proper assessment of the Ayurvedic science is largely dependent upon an understanding of the unified thridosha concept, the significance and real nature of the three humours.

        Vaata (vaayu plus agni), is self-begotten, eternal, and all-pervading. Though invisible, it manifests itself by its properties of coldness, lightness, desiccating action, sound, feel, great speed, angular motion and inconceivable latent power. In its deranged condition it is the principle dosha, because it has the greatest potential of causing damage.

        Pitta (tejas), the cosmic fiery principle, is responsible for the creation of different forms of radiant energy like the body heat (temperature).

        Kapha or sleshma (prithvi plus jala), supplies the placid and cooling principles to the body in the processes of semen formation, growth, nutrition, taste perception, flushing and lubrication of the hard parts, etc.

        The three doshas are further subdivided, into five kinds of each, by some theorists of Ayurveda. Some other theorists also warn us that the thridosha concept is philosophically very involved and that the simplistic equation of the doshas with wind, fire, light, earth and water, does not convey its essentiality completely.

        While the Siddha and the Tibetan systems have humoural concepts similar to that of Ayurveda, the Unani system recognises four humours and the Chinese system only two (see the corresponding sections for the details).

        The deranged thridoshas give rise to specific symptoms affecting the bodily elements in their respective spheres of influences. The distinctive aetiology and prognosis of different diseases are due to the large number of possible permutations and combinations of the three humours, each with five varieties, multiplicity of functions and different possible degrees of provocation. Logically health care lies in primarily detecting the deranged humours and assessing the severity of derangement and secondarily in identifying the specific malady by case history and symptoms. Armed with this knowledge and that of the varied drugs and processes at his command, the Ayurvedic physician can correct the specific imbalance and aggravations and ultimately effect a cure.

        Ayurveda recognises infections and infectivity, but it is argued that the infecting agent is not the real or intrinsic cause of the disease, but only a remote cause. The infecting agent, like all other outside adverse agents, upsets the equilibrium of the doshas in the first instance, this in turn acts on the dhathus, producing the disease and its symptoms.

         Rasa (plasma), rakta (blood), mamsa (muscle), meda (fat), asti (bone), majja (marrow) and shukra (reproductive fluids) are the seven tissue elements (dhathus) of the body. The sapthadhathus interact with agni, the digestive fire, and produce mala, the waste products of the body that are cleared through srotas, the channels of circulation of liquid material in the body.

         According to Ayurveda, life and the biological processes are dependent upon the production of heat inside the organism. The body heat comes from food, which also nourishes and maintains the organism through its metabolic transformations. Ingested food and drink pass into stomach, digested by the digestive juices present there, and form the thin assimilable fluid that turns into rasa, the essence and the nutritive fluid. Through 24 major channels rasa permeates the entire system. Rasa constantly moisturises, nourishes, maintains and irrigates the organism by processes which were not completely understood. It also transquilises, lubricates and vitalises the body. While flowing through the liver and spleen it forms a red colouring matter. The coloured modification of the potent rasa is known as rakta and it is the first metabolic transformation of rasa, which is thereafter successively converted into mamsa, meda, asthi, majja, and finally shukra. Thus food is the source of the sapthadhathus, and digestion and metabolism are the means.