they agreed that a substance’s presence in a spatial location (1) is a positive reality. It was objected:

“If this spatial location is nonexistent, how can a substance conceivably be present in something nonexistent? If it exists, then it is undoubtedly something that can be pointed to (2). It must therefore be either a substance or an accident. If it is a substance, one substance would be present within another substance. This amounts to affirming interpenetration, which is impossible—unless, that is, it is interpreted as contact, concerning which there is no dispute. If it is an accident, then it inheres in a substance; so how can the substance conceivably be present within it?”

Al-Tūsī rebutted this, saying (3): “This error arises from an equivocal use of language. The term (4) ‘in’ conveys different meanings in the statements ‘a body is in another body’—meaning interpenetration—‘a body is in a place,’ and ‘an accident is in a body.’ The first signifies one body being together with another body in a single place; the second signifies a body being in a place; and the third signifies an accident inhering in a body.

“According to some, place is that which admits of dimensions, subsists in itself, and offers no resistance to bodies. According to others, it is an accident: the surface of the [enclosing] (5) body that surrounds the body occupying the place. Its where-ness (6) is self-evident, though its true nature is obscure.”