Some of the Sutras of the six orthodox philosophical systems of the Brahmans refer to Buddhist doctrines and refute them. The author is chiefly concerned with the Sunyavada or philosophical nihilism and with the Vijnanavada or pure idealism. The Sunyavada maintains that all ideas, if analyzed, contain logical impossibilities, and therefore nothing real can underlie them. This system was established by Nagarjuna, who wrote at the end of the second century C.E. The Vijnanavada contends that only consciousness is real. There are two kinds of consciousness: consciousness proper, which lasts until a person reaches Nirvana, and the thoughts of the same person concerning objects. It was established during the latter part of the fifth century C.E. Hermann Jacobi wants to closely examine the Buddhist doctrines disputed in the philosophical Sutras in order to decide whether they belong to the Vijnanavada or the Sinyavada. It was reached that the Sinyavada was composed between 200 and 450 C.E. and the Vijnanavada was compiled later than 450 C.E.