For example, some scholars think that karma was not central to the teaching of the historical Buddha, while other disagree with this position. Likewise, there is scholarly disagreement on whether insight was seen as liberating in early Buddhism or whether it was a later addition to the practice of the four "dhyāna." According to Vetter and Bronkhorst, "dhyāna" constituted the original "liberating practice", while discriminating insight into transiency as a separate path to liberation was a later development."" Scholars such as Bronkhorst and Carol Anderson also think that the four noble truths may not have been formulated in earliest Buddhism but as Anderson writes "emerged as a central teaching in a slightly later period that still preceded the final redactions of the various Buddhist canons."