A citta is not an entity with permanent, actual existence in itself — it is merely a transitory instance of the process of recognizing an object. The characteristic of citta is the ability to recognize an object. Its manifestation is as a continuity of processes. What is usually thought of as consciousness is really series of cittas that arise and disappear in such rapid succession that the discrete events are indistinguishable. Patthana not only distinguishes between types of cittas, but also sets them up in an orderly micro-cosmos — a tightly woven, unified whole of interacting entities.
Besides classifying cittas into the four divisions below: mundane sense sphere, mundane fine-material sphere, mundane immaterial sphere and supramundane, Patthana also classifies cittas according to their nature, which may be unwholesome, wholesome, resultant or functional.
Mundane sense sphere cittas relate to sensuality — both the mental craving for sense pleasures and the objective perception of visible forms, sounds, smells, tastes and touches.
Mundane fine-material sphere cittas relate to the advanced meditative states called rupa jhanas. A rupa jhana state can be achieved by concentrating in meditation on a material object (rupa), which then forms the basis for the jhana state to arise.
Mundane immaterial sphere cittas relate to the even more advanced meditative states called arupa jhanas. To achieve such a state, in meditation one must discard all material objects and instead focus on a non-material object (arupa), e.g. the limitlessness of consciousness or the infinity of the universe.
Supramundane cittas relate to realms beyond the physical universe and beyond all conditioned phenomena, physical and mental. That which transcends the realm of conditioned phenomena is the only unconditioned phenomenon, Nibbana (often called Nirvana). Supramundane cittas are those that can directly lead to the realization of Nibbana.
Unwholesome cittas are consciousness accompanied by one of the three unwholesome roots – greed, hatred or delusion. Such consciousness is called unhealthy because it is mentally unhealthy, morally burdened and produces unpleasant results.
Wholesome cittas, on the other hand, are consciousness accompanied by one of the three wholesome roots – generosity, loving-kindness and non-delusion. Such consciousness is mentally sound, morally blameless and produces pleasant results.
Wholesome as well as unwholesome cittas constitute willful action called kamma (often called karma). The maturation of kamma gives rise to a third class of cittas called resultants. These include the results of both wholesome and unwholesome kamma. However, they themselves do not give rise to any kammic force or effect and are therefore classified as neither healthy nor unhealthy.
A fourth class of cittas is simply called functional. Cittas of this class are neither kamma-generating nor kamma-resultant. They involve activity, but this activity does not generate kammic results and is therefore also outside the concept of wholesome versus unwholesome.
There are a number of different interpretations of what kamma is. In Abhidhamma and Patthana context, kamma and its results are purely mental. Kamma is volitional mind activity associated with wholesome or unwholesome cittas, and kammic results are other cittas experiencing the effects of kamma. In short: in the context of Patthana (the book and this site), kamma is exclusively about the interactions — their causes and consequences — going on in the mind every micro-moment.