  This rejection of a permanent self as the agent of sensory and mental activity posed a significant challenge for the early Buddhists. Indeed, if there is no agent (kartṛ), and if actions (karman) are merely transient events arising within a continuum of causally interconnected states, then how is the efficacy of karma or rebirth to be explained? Historically, at least one Buddhist school, that of the Vātsīputrīyas or Pudgalavādins (‘personalists’), does appear to endorse the reality of persons as conceived in reliance upon the collection of aggregates (see  §5.5  for a detailed discussion). 