It is generally agreed that the eighteen[565] schools were in existence during or shortly before the reign of Asoka, and that six others[566] arose about the same period, but subsequently to them.  The best materials for a study of their opinions are afforded by the text and commentary[567] of the Katha-vatthu, a treatise attributed to Tissa Moggaliputta, who is said to have been President of the Third Council held under Asoka.  It is an examination and refutation of heretical views rather than a description of the bodies that held them but we can judge from it what was the religious atmosphere at the time and the commentary gives some information about various sects.  Many centuries later I-ching tells us that during his visit to India (671-695 A.D.) the principal schools were four in number, with eighteen subdivisions.  These four[568] are the Mahasanghika, the Sthavira (equivalent to the old Theravada), the Mulasarvastivada and the Sammitiya, and from the time of Asoka onwards they throw the remaining divisions into the shade[569].  He adds that it is not determined which of the four should be grouped with the Mahayana and which with the Hinayana, that distinction being probably later in origin.  The differences between the eighteen schools in I-ching’s time were not vital but concerned the composition of the canon and details of discipline.  It was a creditable thing to be versed in the scriptures of them all[570].  It is curious that though the Kathavatthu pays more attention to the opinions of the six new sects than to those held by most of the eighteen, yet this latter number continued to be quoted nearly a thousand years later, whereas the additional six seem forgotten.  It may be that they were more unorthodox than the others and hence required fuller criticism.  Five of their names are geographical designations, but we hear no more of them after the age of Asoka.

The religious horizon of the heretics confuted in the Kathavatthu does not differ materially from that of the Pitakas.  There are many questions about arhatship, its nature, the method of obtaining it and the possibility of losing it.  Also we find registered divergent views respecting the nature of knowledge and sensation.  Of these the most important is the doctrine attributed to the Sammitiyas, that a soul exists in the highest and truest sense.  They are also credited with holding that an arhat can fall from arhatship, that a god can enter the paths or the Order, and that even an unconverted man can get rid of all lust and ill-will[571].  This collection of beliefs is possibly explicable as a result of the view that the condition of the soul, which is continuous from birth to birth, is stronger for good or evil than its surroundings.  The germs of the Mahayana may be detected in the opinions of some sects on the nature of the Buddha and the career of a Bodhisattva.  Thus the Andhakas thought that the Buddha was superhuman in the ordinary affairs of life and the Vetulyakas[572]