to help Subhūti unlearn his preconceived, limited notions of the nature of reality. Emphasizing that all phenomena are ultimately illusory, he teaches that true enlightenment cannot be grasped until one has set aside attachment to them in any form. Another reason why the Buddha makes use of negation is that language reifies concepts and this can lead to attachment to those concepts, but true wisdom is seeing that nothing is fixed or stable, hence according to the Diamond Sūtra thoughts such as "I have obtained the state of an Arhat" or "I will bring living beings to nirvana" do not even occur in an enlightened one's mind because this would be "seizing upon a self ... seizing upon a living being, seizing upon a soul, seizing upon a person". The sutra goes on to state that anyone who says such things should not be called a bodhisattva. According to David Kalupahana the goal of the Diamond Sūtra is "one colossal attempt to avoid the extremist use of language, that is, to eliminate any ontological commitment to concepts while at the same time retaining their pragmatic value, so as not to render them totally empty of meaning". Kalupahana explains the negation of the Diamond Sūtra by seeing an initial statement as an erroneous affirmation of substance or selfhood, which is then critiqued (all dharmas' are dharmaless"), and then finally reconstructed ("that is why they are called 'all dharmas) as being conventional and dependently originated. Kalupahana explains this final reconstruction as meaning: "that each concept, instead of either representing a unique entity or being an empty term, is a substitute for a human experience which is conditioned by a variety of factors. As such, it has pragmatic meaning and communicative power without being absolute in any way." According to Paul Harrison, the Diamond Sūtra central argument here is that "all dharmas lack a self or essence, or to put it in other words, they have no core ontologically, they only appear to exist separately and independently by the power of conventional language, even though they are in fact dependently originated". The mind of someone who practices the Prajñāpāramitā or "perfection of insight" is then a mind free from fixed substantialist or "self" concepts: Throughout the teaching, the Buddha repeats that successful memorization and elucidation of even a four-line extract of it is of incalculable merit, better than giving an entire world system