Clarification of Terms
Many thinkers of all times and climes have insisted that a clarification of concepts and terms must be the basis of all realistic and successful thought, action, and, as Kungfutse says, even of government. But as shown by the widespread confusion of ideas throughout the centuries, this has been neglected in nearly all branches of life and thought - a fact responsible for much of man's unhappiness.
It is another evidence of the scientific spirit of the Abhidhamma that the definition of its terms and of their range of application occupies a very prominent place. In particular, the Dhammasangani is essentially a book of classifications and definitions. In addition, a very elaborate and cautious delimitation of terms is given in the sixth book of Abhidhamma the 'Yamaka', which to our modern taste appears even over-elaborate and over-cautious in that respect.
The Suttas, serving mainly the purpose of offering guidance for the actual daily life of the disciple, are mostly (though not entirely) couched in terms of conventional language (vohara-vacana), making reference to persons, their qualities, possessions, etc. In the Abhidhamma, this Sutta terminology is turned into correct functional forms of thought, which accord with the true 'impersonal' and everchanging nature of actuality; and in that strict, or highest, sense (paramattha) the main tenets of the Dhamma are explained.
While vague definitions and loosely used terms are like blunt tools unfit to do the work they are meant for, while concepts based on wrong notions will necessarily beg the question to be scrutinized and will thus prejudice the issue, the use of appropriate and carefully tempered conceptual tools will greatly facilitate the quest for liberating knowledge, and is an indispensable condition of success in that quest.