The Anatta Doctrine
It is on this very doctrine of Non-self (anatta) that all Abhidhamma thought converges and this is where it culminates. The elaborate and thorough treatment of Anatta is also the most important practical contribution of the Abhidhamma to the progress of the Buddha's disciple towards liberation. The Abhidhamma provides him with ample material for his meditations in the field of insight (vipassana), concerning Impermanence and Impersonality, and this material has been analyzed down to the subtlest point and is couched in strictly philosophical language.
There will certainly be many to whom the degree of analytical details found in the Suttas will be quite enough for them to understand Anatta, and sufficient for their use in meditative practice. But there are also minds that require repeated and varied demonstration and illustration of a truth before they are entirely satisfied and convinced. There are also others who wish to push their analysis to the greatest detail possible and to extend it to the very smallest unit accessible; in order to make quite sure that even the realm of the infinitesimal, of the material and psychical 'atoms', does not hide any self or abiding substance. To such minds the Abhidhamma will be of great value. But also those who, in general, are satisfied with the expositions in the Suttas, may sometimes wish to investigate more closely a particular point that has roused their interest or presents difficulties. To them too the Abhidhamma will prove helpful.
Besides helping such individual cases, the Abhidhamma will in general render valuable aid in the slow and difficult change of thought and outlook from the view-point of 'self' to that of 'non-self'. Having once grasped intellectually the doctrine of non-self, one can certainly succeed in applying it to theoretical and practical issues if only one remembers it in time and deliberately directs one's thoughts and volitions accordingly. But except for such deliberate directing of thought, which in most cases will be relatively rare, the mind will continue to move in the old-accustomed ruts of 'I' and 'mine', 'self' and 'substance', which are deeply ingrained in our daily language and our modes of thinking; and our actions too will still continue to be frequently governed by our ancient egocentric impulses. An occasional intellectual assent to the true outlook of Anatta will not effect great changes in that situation. The only remedy is for bad or wrong habits of action, speech and thinking to be gradually replaced by good and correct habits until the latter become as spontaneous as the former are now. It is therefore necessary that right thinking, that is, thinking in terms of Anatta, is made the subject of regular and systematic mental training until the power of wrong habits of thought is reduced and finally broken. The Abhidhamma in general, and in particular the various Triads and Dyads of terms as listed in the Matika, 'Schedule', of the Abhidhamma Pitaka, provide ample material for such 'fluency exercises' of right thinking. Familiarity with the application of the 'impersonal' view-point of the Abhidhamma and with the terminology by which it is expressed will exercise a considerable formative influence on the mind.