The abstract reason is perhaps the most uniquely human capability, relying on the intellect to analyze, discriminate and define things. When applied to the process of realisation, this power provides both its unique strengths and its limiting weaknesses. The strengths of the abstract intellectual reason is that it provides an actual opportunity to escape the bondage of everyday affairs and thus, provide an opportunity for a further development and a new standpoint. It does this through systematically reviewing each thing, whether a material form, or a force, or a thought, and determining if it is limited or unlimited, finite or infinite; and to the extent it determines the limitations, it excludes those forms, forces or ideas. Eventually, it is forced to eliminate everything in manifestation and develop a statement such as we find in the Upanishads at one point, “neti, neti” (“not this, not that”). What the intellect is then left with is an abandonment of action and an increasing stillness, to achieve unification with the Eternal in the form of the unmoving, infinite, and dispassionate stillness of Eternity.
Few are those who are capable of carrying out such an austere path of knowledge. For those, there is no doubt a realisation at the end which has been called Nirvana, or perhaps Nirvikalpa Samadhi (Samadhi without “seed”) from which there is no returning.
The limitation here, besides the fact that few actually can tread this path successfully, is that it does not address either the purpose or reality of the universe, nor the complex human being composed of capabilities and forces other than the pure abstract intellect. It convicts the Creation of being an illusion, a distraction or an irrelevancy. It essentially also forgets that by using a process of negation, it fails to solve the affirmative side. It essential forgets the other great Upanishadic dictum: “All this is the Brahman.”
Sri Aurobindo summarizes: “It negates life in order to return to its source, cuts away from us all that we seem to be in order to get from it to the nameless and impersonal reality of our being. The desires of the heart, the works of the will and the conceptions of the mind are rejected; even in the end knowledge itself is negated and abolished in the Identical and Unknowable.”
Sri Aurobindo, Essays on the Gita, Second Series, Part I, Chapter 7, The Supreme Word of the Gita, pg. 324