Is Space Within the Three Realms or Beyond Them?

The reasoning for this question is as follows: first, clarify the concepts and characteristics of space and the three realms along with the six sense faculties, then determine whether space belongs to the dharmas of the three realms, thereby arriving at a true and correct conclusion. The meaning of space is emptiness or void, primarily constituted by the element of space. Space constituted by the element of space is also called spatial void, characterized by its capacity to contain and support, possessing practical functions to accommodate and bear material form dharmas. Since it is constituted by the element of space among the four great elements, space is a form dharma, possessing characteristics—specifically, the characteristic of emptiness and absence of substance.

Space is a form dharma, belonging to the form at the boundary of form. It is seen by the eye consciousness. Form dharmas seen by the eye consciousness must possess characteristics; however, space possesses the characteristic of emptiness and absence, while material form dharmas possess the characteristic of non-emptiness and presence. This is explained in the Yogācārabhūmi-śāstra. The characteristic of "form at the boundary of form" differs from that of form dharmas. Upon opening the eyes, one immediately knows whether what lies before them is empty or not. Emptiness, as a form dharma, is seen by the eye consciousness, and non-empty form dharmas are also seen by the eye consciousness. Emptiness has its own characteristic of emptiness, while non-empty material form dharmas have their own characteristic of non-emptiness. If emptiness had no characteristic, how could the eye consciousness recognize whether it is empty or not?

The definition of the three realms is that they consist of dharmas, not emptiness; they include form dharmas, mind dharmas, and neither-form-nor-mind dharmas. Mind dharmas and form dharmas are two distinct boundaries, mutually exclusive. However, form dharmas are the form dharmas within the mind, not dharmas external to the mind. Space is also a dharma within the mind, not external to it. Space is also a dharma, not a non-dharma; therefore, space belongs to the dharmas of the three realms. There is only one dharma not within the three realms: the self-nature true mind. Since space is a form dharma, possesses function, and can support material form dharmas, space certainly resides within the three realms, not outside them. Outside the three realms, there is definitely no space.

Space is the emptiness of spatial void. "Tortoise hair and rabbit horns" represent the nothingness of absolute non-existence and non-existent emptiness, not the emptiness of space. Therefore, tortoise hair and rabbit horns do not pertain to being within or outside the three realms. Space has no boundaries; the worlds of the ten directions all exist within space. The three realms have boundaries; existence and nothingness constitute the boundaries of the three realms. The three realms are suffering; reaching the boundary of suffering, where there is no longer form dharmas or the seven consciousnesses' mind dharmas, is the state of Nirvāṇa without residue—this is the boundary of the three realms. Nirvāṇa and non-Nirvāṇa mark the boundary line. Although the mind dharmas of the seven consciousnesses do not reside within space, they are dharmas within the three realms. Tathāgatagarbha is not a dharma within the three realms, nor is it a dharma outside the three realms, because there are no dharmas outside the three realms. Arhats who have attained Nirvāṇa, having no form dharmas or the seven consciousnesses' mind dharmas, do not dwell within space. Only form dharmas can dwell within space, yet they do not reside within the three realms.