The various schools of Indian philosophies vary on how many of these six are epistemically reliable and valid means to knowledge. For example, Carvaka school of Hinduism holds that only one (perception) is a reliable source of knowledge, Buddhism holds two (perception, inference) are valid means, Jainism holds three (perception, inference and testimony), while Mimamsa and Advaita Vedanta schools of Hinduism hold all six are useful and can be reliable means to knowledge. The various schools of Indian philosophy have debated whether one of the six forms of "pramana" can be derived from other, and the relative uniqueness of each. For example, Buddhism considers Buddha and other "valid persons", "valid scriptures" and "valid minds" as indisputable, but that such testimony is a form of perception and inference "pramanas".