 The texts of the canonical Abhidharma are works that evolved over decades, if not centuries, out of materials already present in the Sūtra and Vinaya portions of the canon. This is evidenced in two characteristics of the genre that can be traced to earlier Buddhist literature. The first is the analytical style of the texts, which attempt to summarize meticulously the significant points of the Dharma and provide a comprehensive taxonomy of the mental and physical factors that constitute sentient experience. This analytical enterprise includes the arrangement of major parts of the material around detailed lists of factors and combinations of sets of their categories yielding matrices (Skt., mātṛkā, Pali, mātikā) of doctrinal topics. Already in the collections of the Buddha’s discourses, certain texts are arranged according to taxonomic lists, providing formulaic treatment of doctrinal items that are expounded elsewhere. Lists were clearly powerful mnemonic devices, and their prevalence in early Buddhist literature can be explained partly as a consequence of its being composed and for some centuries preserved  orally.[5]  For instance, one of the four primary Āgamas/Nikāyas, the collection of “grouped” sayings (saṃyukta/saṃyutta), groups the Buddha’s teachings according to specific topics, including the four noble truths, the four ways of establishing mindfulness, the five aggregates, the six sense faculties, the seven constituents of awakening, the noble eightfold path, the twelve links of dependent origination, and others. Similar taxonomic lists form the table of contents of the Vibhaṅga and Puggalapaññatti of the Theravāda and the Saṅgītiparyāya and Dharmaskandha of the Sarvāstivāda, which are structured as commentaries on those lists.