Each new ontological theory, propounded in lieu of previous...

Each new ontological theory, propounded in lieu of previous ones shown to be untenable, has been followed by a new criticism leading to a new scepticism. All possible conceptions have been one by one tried and found wanting; and so the entire field of speculation has been gradually exhausted without positive result: the only result reached being the negative one above stated, that the reality existing behind all appearances is, and must ever be, unknown.