Why does the Tathāgata have no fixed dharma to expound?

Original text of the Diamond Sutra: 须菩提言。如我解佛所说义。无有定法。名阿耨多罗三藐三菩提。也无有定法。如来可说。何以故。如来所说法。皆不可取。不可说。非法。非非法。一切圣贤皆以无为法而有差别。

The explanation of this passage is as follows: Subhūti replied to the Buddha: According to my understanding of the meaning of what the Buddha taught, there is no fixed dharma called anuttarā-samyak-saṃbodhi, and there is no substantially existent dharma called anuttarā-samyak-saṃbodhi. Why is this said? Because anuttarā-samyak-saṃbodhi is also called unsurpassed, complete, perfect enlightenment, that is, the accomplishment of the Buddha Way. Becoming a Buddha is not something innately existing, a fixed and unchanging dharma; it is achieved later through cultivation over three great asaṃkhyeya kalpas. Therefore it is also subject to arising and ceasing, coming into being from non-being; hence it is not a fixed dharma, nor a substantially existent dharma.

Nor is there any fixed dharma that the Tathāgata can teach. Why is this said? Because the Tripitaka and twelve divisions of scriptures that the Tathāgata taught over forty-nine years in the Sahā world cannot be grasped as substantially existent; indeed, all the dharmas the Tathāgata taught in the worlds of the ten directions cannot be grasped as substantially existent. Why can they not be grasped as substantially existent? Because all the dharmas the Buddha taught arose due to various conditions and causes. Without causes and conditions, these dharmas would not exist, and the Buddha would not teach any dharma. Even such a great matter as the Buddha's saving of sentient beings requires the ripening and completeness of causes and conditions, requiring sentient beings' merit, causes and conditions of good roots, and the aspiration for liberation, and so on. Lacking even one condition, the Buddha cannot save sentient beings. And the dharma taught to save sentient beings is determined according to conditions, determined according to sentient beings' indriya, merit, and wisdom; there is no fixed dharma to be taught.

A fixed dharma means a dharma that is fixed and unchanging, originally existing, that does not turn with causes and conditions, does not vary with causes and conditions—a truly real, unchanging dharma, where the same dharma is used for all sentient beings regardless, regardless of what faculties sentient beings have, and regardless of what conditions arise, the same dharma is used. Clearly, this is wrong, unachievable, and unworkable; no such dharma exists. Dharmas produced by causes and conditions, not innately existing dharmas, are not fixed dharmas. Therefore it is said that the Tathāgata, in saving sentient beings, has no fixed dharma to teach.

Therefore, the dharma taught by the Tathāgata cannot be spoken of as a substantially existent, unchanging dharma; it is also a dharma subject to arising, ceasing, and change, coming from non-being into being, from being into non-being, a raft to be abandoned upon reaching the shore. It is also an empty dharma; hence it is merely named "dharma." In reality, dharmas have no self-nature, no self-substance to be spoken of; therefore it is not-dharma (a-dharma). Yet it is also not entirely not-dharma, for after all there is its illusory function: a provisional dharma can nevertheless be provisionally used and borrowed; sentient beings using it can attain buddhahood, and after attaining buddhahood, they then discard it. Therefore the dharma taught by the Buddha is also not-not-dharma; it is not that it is not dharma.

Since all the dharma taught by the Tathāgata is not-dharma, being dharmas produced by causes and conditions, with no fixed dharma, then when the Tathāgata teaches different dharmas to sentient beings of different indriya according to different conditions, and sentient beings cultivate and study them, they realize unconditioned dharmas of different levels—including the unconditioned of the Great, Middle, and Small Vehicles, and even within the same vehicle there are differences among unconditioned dharmas. Thus sages and worthies of different levels and different distinctions are accomplished. All sages and worthies, because of differences in good roots, merit, and conditions, differ according to the unconditioned dharma they have realized.