According to Abhidhamma ordinarily there is no moment when we do not experience a particular kind of consciousness, hanging on to some object - whether physical of mental. The time-limit of such a consciousness is termed one thought-moment. The rapidity of the succession of such thought-moments is hardly conceivable by the ken of human knowledge. Books state that within the brief duration of a flash of lightning, or in the twinkling of an eye billions of thought-moments may arise and perish.

Each thought-moment consists of three minor instants (khaṇas). They are uppāda (arising or genesis), ṭhiti (static or development), and bhaṅga (cessation or dissolution).

Birth, decay, and death* correspond to these three states. The interval between birth and death is regarded as decay.

Immediately after the cessation stage of a thought-moment there results the genesis stage of the subsequent thought-moment. Thus each unit of consciousness perishes conditioning another, transmitting at the same time all its potentialities to its successor. There is, therefore, a continuous flow of consciousness like a stream without any interruption.

[*These three stages correspond to the Hindu view of Brahma (Creator). Vishnu (Preserver) and Siva (Destroyer).]

When a material object is presented to the mind through one of the five sense-doors, a thought-process occurs, consisting of a series of separate thought-moments leading one to the other in a particular, uniform order. This order is known as the citta-niyāma (psychic order). As a rule for a complete perception of a physical object through one of the sense-doors precisely 17 thought-moments must pass. As such the time duration of matter is fixed at 17 thought-moments. After the expiration of that time-limit, one fundamental unit of matter perishes giving birth to another unit. The first moment is regarded as the genesis (uppāda), the last as dissolution (bhaṅga), and the interval 15 moments as decay or development (ṭhiti or jarā).

As a rule when an object enters the consciousness through any of the doors one moment of the life-continuum elapses. This is known as atīta-bhavaṅga. Then the corresponding thought-process runs uninterruptedly for 16 thought-moments. The object thus presented is regarded as 'very great.'

If the thought-process ceases at the expiration of javanas without giving rise to two retentive moments (tadālambana), thus completing only 14 moments, then the object is called 'great'.

Sometimes the thought-process ceases at the moment of determining (votthapana) without giving rise to the javanas, completing only 7 thought-moments Then the object is termed 'slight.'

At times when an object enters the consciousness there is merely a vibration of the life-continuum. Then the object is termed 'very slight.'

When a so-called 'very great' or 'great' object perceived through the five sense-doors, is subsequently conceived by the mind-door, or when a thought process arising through the mind-door extends up to the retentive stage, then the object is regarded as 'clear'.

When a thought process, arising through the mind-door, ceases at the javana stage, the object is termed 'obscure'.

When, for instance, a person looks at the radiant moon on a cloudless night, he gets a faint glimpse of the surrounding stars as well. He focuses his attention on the moon, but he cannot avoid the sight of stars around. The moon is regarded as a great object, while the stars are regarded as minor objects. Both moon and stars are perceived by the mind at different moments. According to Abhidhamma it is not correct to say that the stars are perceived by the sub-consciousness and the moon by the consciousness.