The image in the mirror of the tathāgatagarbha is also material form

All dharmas are divided into material form, mind dharmas, and dharmas that are neither form nor mind. Material form is necessarily composed of the four great seeds (earth, water, fire, and wind), and is the portion perceived by mind dharmas. The image seen in a mirror by consciousness is also material form, necessarily composed of the four great seeds; only the structure of its composition differs somewhat from the material form outside the mirror. Mind dharmas are the minds capable of discrimination, whereas the image in the mirror cannot discriminate, and therefore is not a mind dharma.

The appearances outside the mirror are jointly manifested by the tathāgatagarbhas of sentient beings with shared karma, while the image upon the mirror is manifested by an individual sentient being's tathāgatagarbha in dependence on the appearances outside. The appearances outside the mirror are false, and the image upon the mirror is even more false. The appearances at various levels differ in the subtle particles composed of the four great seeds, resulting in different degrees of reality. Everything of our own material bodies that we ourselves see is like the image upon the mirror. Does it exist or not exist? Is it neither existent nor non-existent? Or is it neither non-existent nor not non-existent?

In the Śūraṅgama Sūtra, the Buddha said that the subtle dust of the material body and the subtle dust of the inanimate world are not two and not different, being composed of the same four great seeds. For example, the garbage and waste expelled daily from the body through blood vessels and skin is exactly the same as the sand and soil of the inanimate world; the sweat expelled is exactly the same as the water of nature; the breath exhaled from the mouth, nose, and skin is exactly the same as the wind of the inanimate world; and the fiery energy radiating from the body is exactly the same as the fire of the inanimate world. Therefore, the four great seeds composing material form are identical, and the body and the inanimate world are not two and not different. When the external four great elements undergo change, the body changes accordingly.

As for the non-Buddhists' doctrine of non-existence: they see material form with their eyes, yet claim it does not exist. If it were non-existent, why is there any verbal discourse about it? As for the non-Buddhists' doctrine of existence: although all material form is manifestly impermanent and empty, they claim it is real and indestructible. The Dharma taught by the Buddha is neither existent nor non-existent, neither existent nor non-existent [in the sense of being beyond both], both existent and non-existent, and neither non-existent nor not non-existent. To grasp only one of these aspects while disregarding the rest is the view of non-Buddhists. The Buddha's Dharma is always perfectly all-encompassing—stated from the left or stated from the right, it always holds true. The doctrines of non-Buddhists, however, can never be made self-consistent and are always self-contradictory.