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

All dharmas are divided into material form (rūpa-dharma), mental dharmas (citta-dharma), and dharmas that are neither material nor mental. Material form is necessarily composed of the seeds of the four great elements, and is the part perceived by mental dharmas. The image seen in a mirror by the conscious mind is also material form, necessarily composed of the seeds of the four great elements; only its compositional structure differs somewhat from the material form outside the mirror. Mental dharma is the mind that can discriminate, whereas the image in the mirror cannot discriminate; therefore it is not a mental dharma.

The appearances outside the mirror are jointly manifested by the tathāgatagarbhas of sentient beings sharing common karma, while the image on 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 on the mirror is even more false. The appearances at various levels differ in the particles composed of the seeds of the four great elements, resulting in different degrees of reality. Everything of our own material body that we ourselves see is like the image on 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 particles of dust of the material body and the particles of dust of the inanimate world are not two and not different; they are composed of the same seeds of the four great elements. For example, the garbage and waste expelled every day from the blood vessels and skin of the body 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 heat emitted by the body is exactly the same as the fire of the inanimate world. Therefore, the seeds of the four great elements composing material form are identical, and the body and the inanimate world are not two and not different. When the four great elements of the external world change, the body changes accordingly.

As for the non-Buddhists' thesis of non-existence: they see material form with their eyes, yet say it does not exist. If it is non-existent, why is there any verbal assertion? As for the non-Buddhists' thesis of existence: although all material form is clearly impermanent and empty, they say it is real and indestructible. The Dharma taught by the Buddha is neither existent nor non-existent, neither existent nor non-existent [in the double-negation sense], both existent and non-existent, and neither non-existent nor not non-existent. To take only one of these positions while disregarding the rest is the non-Buddhist view. The Buddha's Dharma is always perfectly penetrating—whether stated one way or another, it all holds true. The non-Buddhists' theories, however, can never be self-consistent and are always self-contradictory.