Rasana

That taste should count as a fundamental principle of reality, on equal footing with sight or hearing, is a specifically Samkhya commitment worth pausing on, since most philosophical systems that enumerate basic categories of existence do not give the sense of taste its own dedicated slot at all. Rasana, the tongue's underlying faculty, is exactly as fundamental in this scheme as chakshu or shrotra: each of the five Jnanendriyas is one of twenty-five tattvas, no more and no less basic than the others, and rasana's single tanmatra, rasa, is treated as a real feature of the material world rather than as a merely subjective sensation layered onto it afterward.

Rasa, the tanmatra rasana perceives, sits fourth among the five in most orderings, denser than shabda, sparsha and rupa, subtler only than gandha, smell. This position places rasana's corresponding gross element, apas, water, near the bottom of the elemental sequence, and Indian cosmological writing generally credits water with carrying flavour distinctively, food and drink dissolved in or mixed with water being where taste is most readily experienced, a correspondence the tattva chain states as a structural fact rather than as observation alone.

Because rasana, like the other Jnanendriyas, is produced from the sattvic aspect of ahamkara, it shares their purely receptive character: it registers rasa, contributes that registration to manas for synthesis with the other senses, and does nothing further. The active complement to eating and tasting, in this scheme, belongs elsewhere, to payu and to the Karmendriyas generally, keeping Samkhya's strict division between perceiving and acting intact even in a function as physically involved as eating.

Rasana's tanmatra, rasa, is the fourth link in the chain that ends in the five gross elements, and the element it feeds is apas, water, traditionally described as having taste for its sense and flavour, rasa, for its subtle quality, drawn from the same body of Samkhya literature this entry draws from. Rasana is the organ-side half of that pairing: the perceptual faculty whose sole object, flavour, is also the quality water specifically contributes once enough tanmatras have accumulated for it to condense out of the evolutionary sequence.

The correspondence is not merely thematic. Samkhya's account of grossening is cumulative, each gross element carrying the tanmatra qualities of every element before it in the sequence plus one of its own, so water carries sound, touch and form in addition to its own distinctive taste, while fire, one step earlier, carries sound, touch and form but not yet taste. This is why taste is described as first becoming perceptible at the level of water rather than at the level of fire or air: it is literally the newest quality water's position in the sequence contributes.

Rasana's place fourth among the five Jnanendriyas, and its narrow restriction to rasa alone, both follow directly from this structure. An organ built to register a quality that only becomes available at the fourth stage of grossening has no occasion to register anything earlier or later in the sequence, which is exactly the strict one-to-one discipline Samkhya maintains across all five organ-tanmatra-element chains.