Kalāpa: 'group', 'unit': 1. 'material unit' see: rūpa-kalāpa 2. It has the meaning of 'group of existence' khandha in kalāpasammasana see: i.e. 'comprehension by groups', which is the application of 'methodical or inductive insight' naya-vipassanā to the comprehension of the 5 aggregates or clusters khandha as impermanent, painful and no-self. It is a process of methodical summarization, or generalization, from one's own meditative experience that is applied to each of the 5 aggregates or clusters, viewed as past, present, future, as internal and external, etc. In Vis.M XX, where the 'comprehension by groups' is treated in detail, it is said to constitute 'the beginning of insight' as it leads to the 'knowledge of rise and fall', being the first of the 8 insightknowledges see: visuddhi VI. It is necessary for accomplishing the 5th purification.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.