Inconsistencies in the oldest texts show that the Buddhist teachings on craving and ignorance, and the means to attain liberation, evolved, either during the lifetime of the Buddha, or thereafter. According to Frauwallner, the Buddhist texts show a shift in the explanation of the root cause of samsara. Originally craving was considered to be the root cause of samsara, which could be stilled by the practice of "dhyana", leading to a calm of mind which according to Vetter "is" the liberation which is being sought.