Abhidhamma is mainly concerned with the study of abstract truths in absolute terms. But in describing the dhammas in their various aspects, it is not possible to keep to absolute terms only. Inevitably, conventional terms of every day language have to be employed in order to keep the lines of communication open at all. Abhidhamma states that there are two main types of conventional usage; the first type is concerned with terms which express things that actually exist in reality and the second type describes things which have no existence in reality.
The first three books of the Abhidhamma investigate the absolute Truth of Dhamma in a planned system of detailed analysis employing such terms as Khandha, Æyatana, Dhætu, Sacca and Indriya. These terms are mere designations which express things that exist in reality and are therefore classed as the conventional usage of the first type. To the second type of conventional usage belong such expressions as man, woman, deva, individual etc., which have no existence in reality, but nevertheless are essential for communication of thoughts.
It becomes necessary therefore to distinguish between these two types of apparent truths. But as the terms Khandha, Æyatana, Dhætu, Sacca and Indriya have been elaborately dealt with in the first three books, they are dealt with here only briefly. The terms used in the second type concerning individuals are given more weight and space in the treatise, hence its title Puggalapaññatti, designation of individuals. Different types of individuals are classified, in ten chapters of the book, after the manner of enumeration employed in A³guttara Nikæya.