The Abhidhamma Pitaka (abhidhammapiṭaka) is the last of the three pitakas (Pali for "baskets") constituting the Pali Canon, the scriptures of Theravāda Buddhism.
The Abhidhamma Pitaka is a detailed scholastic reworking of material appearing in the Suttas, according to schematic classifications. It does not contain systematic philosophical treatises, but summaries or enumerated lists.
The other two collections are the Sutta Pitaka and the Vinaya Pitaka.
Abhidhamma has been variously described as philosophy, psychology, and metaphysics. L. S. Cousins says that the Abhidhamma methodology looks at things in terms of occasions or events instead of sequences or processes.
Tradition holds that the Buddha thought out the Abhidhamma immediately after his enlightenment then taught it to the gods some years later. Later the Buddha repeated it to Sariputta who then handed it on to his disciples. This tradition is also evident in the Parivara, a very late addition to the Vinaya Pitaka, which mentions in a concluding verse of praise to the Buddha that this best of creatures, the lion, taught the three pitakas..
Scholars, however, generally date the Abhidhamma works to originating some time around the third century BCE, 100 to 200 years after the death of the Buddha. Therefore, the seven Abhidhamma works are generally claimed by scholars not to represent the words of the Buddha himself, but those of disciples and scholars. Dr Rupert Gethin however said that important elements of Abhidhamma methodology probably go back to the Buddha's lifetime. A. K. Warder and Dr Peter Harvey both suggested early dates for the matikas on which most of the Abidhamma books are based. Abhidhamma started out as elaboration of the suttas, but later developed independent doctrines.
As the last major division of the canon, the Abhidhamma Pitaka has had a checkered history. It was not accepted as canonical by the Mahasanghika school and several other schools. Another school included most of the Khuddaka Nikaya within the Abhidhamma Pitaka. Also, the Pali version of the Abhidhamma is a strictly Theravada collection, and has little in common with the Abhidhamma works recognized by other Buddhist schools. The various Abhidhamma philosophies of the various early schools have no agreement on doctrine and belong to the period of 'Divided Buddhism' (as opposed to Undivided Buddhism). The earliest texts of the Pali Canon have no mention of (the texts of) the Abhidhamma Pitaka. The Abhidhamma is also not mentioned in some reports of the First Buddhist Council, which do mention the existence of the texts of the Vinaya and either the five Nikayas or the four Agamas, although it may be noted that the Venerable [Sariputra] foremost in Abhidhamma had passed on before the Buddha before the First Council took place. Other accounts do include the Abhidhamma.
In the Theravadin Abhidhamma Pitaka, unlike the Abhidharma Pitaka of the Sarvastivada school, ontological theorizing is absent, and the question of ontological status of dharmas remains a moot point. The notion of sabhava (Sanskrit: svabhava) is only utilized in late Theravadin texts. The doctrine of momentariness is also a late addition to Theravada thought. It only appears at the time of Buddhaghosa.
The Abhidhamma Piṭaka consists of seven books:Dhammasaṅganī (-saṅgaṇi or -saṅgaṇī)
The Dhammasangani (Summary of Dharma) is a manual of ethics for monks. It begins with a mātikā (translated as matrix) which lists classifications of dhammas (translated as phenomena, ideas, states, etc.). The mātikā starts with 22 threefold classifications, such as good/bad/unclassified, and then follows with 100 twofold classifications according to the Abhidhamma method. Many of these classifications are not exhaustive, and some are not even exclusive. The mātikā ends with 42 twofold classifications according to the sutta method; these 42 are only used in the Dhammasangani, whereas the other 122 are used in some of the other books as well.
The main body of the Dhammasangani is in four parts. The first part goes through numerous states of mind, listing and defining by lists of synonyms, factors present in the states. The second deals with material form, beginning with its own mātikā, classifying by ones, twos and so on, and explaining afterwards. The third explains the book's mātikā in terms of the first two parts, as does the fourth, by a different method (and omitting the sutta method).
The Vibhanga (Division or Classification) consists of 18 chapters, each dealing with a different topic. For example, the first chapter deals with the five aggregates. A typical chapter consists of three parts. The first of these parts explains the topic according to the sutta method, often word-for-word as in actual suttas. The second is Abhidhamma explanation, mainly by lists of synonyms as in the Dhammasangani. The third employs questions and answers, based on the mātikā, such as "How many aggregates are good?"
The Dhatukatha (Discussion of Elements) covers both the matika and various topics, mostly from the Vibhanga, relating them to the 5 aggregates, 12 bases and 18 elements. The first chapter is fairly simple: "In how many aggregates etc. are good dhammas etc. included?" The book progressively works up to more complicated questions: "From how many aggregates etc. are the dhammas dissociated from attention etc. dissociated?"
The Puggalapannatti (Designation of Person) starts with its own matika, which begins with some standard lists but then continues with lists of persons grouped numerically from ones to tens. This latter portion of the matika is then explained in the main body of the work. It lists human characteristics encountered on the stages of a Buddhist path. Most of the lists of persons and many of the explanations are also found in the Anguttara Nikaya.
The Kathavatthu (Points of Controversy) consists of more than two hundred debates on questions of doctrine. The questions are heretical in nature, and are answered in such a way as to refute them. It starts with the question of whether or not a soul exists. It does not identify the participants. The commentary says the debates are between the Theravada and other schools, which it identifies in each case. These identifications are mostly consistent with what is known from other sources about the doctrines of different schools. It is the only portion attributed to a specific author, Moggaliputta.
The Yamaka (Pairs) consists of ten chapters, each dealing with a different topic; for example, the first deals with roots. A typical chapter (there are a number of divergences from this pattern) is in three parts. The first part deals with questions of identity: "Is good root root?" "But is root good root?" The entire Yamaka consists of such pairs of converse questions, with their answers. Hence its name, which means pairs. The second part deals with arising: "For someone for whom the form aggregate arises, does the feeling aggregate arise?" The third part deals with understanding: "Does someone who understands the eye base understand the ear base?" In essence, it is dealing with psychological phenomena.
Patthan (Activations or Causes) deals with 24 conditions in relation to the matika: "Good dhamma is related to good dhamma by root condition", with details and numbers of answers.
The importance of the Abhidhamma Pitaka in classical Sinhalese Buddhism is suggested by the fact that it came to be furnished, not only, like much of the canon, with a commentary and a subcommentary on that commentary, but even with a subsubcommentary on that subcommentary. In more recent centuries, Burma has become the main centre of Abhidhamma studies. However, all of Southeast Asia and Sri Lanka hold it in high regard.
The first five books and part of the seventh of the Abhidhamma Pitaka have been translated by the Pali Text Society, which offers an option to order them through their website.