Mahayanist metaphysics, like all other departments of this theology, are beset by the difficulty that the authorities who treat of them are not always in accord and do not pretend to be in accord. The idea that variety is permissible in belief and conduct is deeply rooted in later Buddhism: there are many vehicles, some better than others no doubt and some very ramshackle, but all are capable of conveying their passengers to salvation. Nominally the Mahayana was divided into only two schools of philosophy: practically every important treatise propounds a system with features of its own. The two schools are the Yogâcâras and Mâdhyamikas.[101] Both are idealists and deny the reality of the external world, but whereas the Yogâcâras (also called Vijñânavâdins) admit that Vijñâna or consciousness and the series of states of which it consists are real, the Mâdhyamikas refuse the title of reality to both the subjective and the objective world and hence gained a reputation of being complete nihilists. Probably the Mâdhyamikas are the older school. Both schools attach importance to the distinction between relative and absolute knowledge. Relative knowledge is true for human beings living in the world: that is to say it is not more false than the world of appearance in which they live. The Hinayanist doctrines are true in this sense. Absolute knowledge rises above the world of appearance and is altogether true but difficult to express in words. The Yogâcâra makes three divisions, dividing the inferior knowledge into two. It distinguishes first illusory knowledge (_parikalpita_) such as mistaking a piece of rope for a snake or belief in the existence of individual souls. Secondly knowledge which depends on the relations of things (_paratantra_) and which though not absolutely wrong is necessarily limited, such as belief in the real existence of ropes and snakes. And thirdly absolute knowledge (_parinishpanna_), which understands all things as the manifestation of an underlying principle. The Mâdhyamikas more simply divide knowledge into _samvṛiti-satya_ and _paramârtha-satya_, that is the truth of every-day life and transcendental truth. The world and ordinary religion with its doctrines and injunctions about good works are real and true as _samvṛiti_ but in absolute truth (_paramârtham_) we attain Nirvana and then the world with its human Buddhas and its gods exists no more. The word _śûnyam_ or _śûnyatâ_, that is _void_, is often used as the equivalent of _paramârtham_. Void must be understood as meaning not an abyss of nothingness but that which is found to be devoid of all the attributes which we try to ascribe to it. The world of ordinary experience is not void, for a great number of statements can be made about it, but absolute truth is void, because nothing whatever can be predicated of it. Yet even this colourless designation is not perfectly accurate,[102] because neither being nor not-being can be predicated of absolute truth.