Definitions
Cittas: In Abhidhamma philosophy and Buddhist phenomenology, cittas are defined as discrete, momentary states of consciousness or primary acts of cognition that arise and pass away in a rapid, continuous stream (citta-vīthi). Rather than denoting a static entity or a permanent "mind," a citta represents the bare, subjective experience of cognizing an intentional object (ārammana). Each citta is an atomic event of awareness that never occurs in isolation; it is always conditioned by and co-arises with a specific constellation of concomitant mental factors (cetasikas), which qualify its ethical quality and psychological function.
Mundane (Lokiya): In the context of cittas, the term "mundane" denotes any state of consciousness that is structurally bound to the conditioned realms of existence (saṃsāra), specifically the sensory, fine-material, and immaterial spheres. Academically, it indicates that the consciousness cognizes an object that is subject to impermanence, suffering, and non-self, rather than the unconditioned element (Nibbāna). Consequently, mundane cittas remain subject to cognitive distortions and mental fermentations (āsavas), and they actively participate in the generation or experience of karmic resultants (vipāka) within the cycle of rebirth.
Sphere (Āvacara): In the taxonomy of cittas, a "sphere" denotes a specific frequency, plane, or structural domain of consciousness and its corresponding experiential reality. It defines the qualitative boundary and cognitive scope of a mind-state, categorized into the sense-sphere (kāmāvacara), fine-material sphere (rūpāvacara), and immaterial sphere (arūpāvacara). Academically, a sphere indicates both a psychological dimension—the level of meditative absorption or sensory engagement a citta operates within—and the ontological realm of existence where such consciousness typically arises and finds its objective footing.