Which transformation involves subtracting a portion of a form's volume?

The correct answer reflects the process of a subtractive transformation, which is characterized by the removal or subtraction of portions of a form's volume. This transformation typically results in new spatial configurations and can help define both interior and exterior spaces.

In architecture, subtractive transformations are often employed to create voids or openings in a solid mass, leading to innovative designs. This method allows architects to manipulate forms meaningfully, enhancing the overall composition and functional aspects of a structure.

The other options describe different concepts. Additive transformation implies the addition of material or volume, which focuses on growth rather than reduction. Dimensional transformation usually pertains to alterations in the size or scale of a form without specifically indicating volume removal. Transformative alteration could refer to a general change in form but does not specifically highlight the subtractive nature of the transformation process. Thus, among the choices presented, subtractive transformation is the only one that accurately describes the act of taking away part of a volume.