The mental factors (caitasika-dharmas) are the mental activities of the mind king (citta)

When the seeds of consciousness flow out, they form the substance of the mind-king (citta-rāja). The substance of the mind-king is pure, because the seeds of consciousness are pure. The seeds of consciousness have no defiled nature, nor any wholesome or unwholesome nature; but when they conjoin with the mental factors (caittas) and operate in the form of mental factors, wholesome, unwholesome, and neither-wholesome-nor-unwholesome mental activities appear. Therefore, the mental activities of the eight mind-kings and the mental activities of the mental factors are in fact one and the same: the mental factors are the mental activities of the mind-kings. When the eight mind-kings operate, they operate in the form of mental factors—especially in the form of the five universally present mental factors (pañca-samprayukta-caitta).