One of the central tensions within the literature on body studies concerns the degree to which the physical body is constituted by or through language, knowledges, and practices and the degree to which the body has foundational, purely material, or essential attributes. Three theoretical approaches have been at the heart of this debate: social constructionism, phenomenology, and structuration theory. Recently, body studies theorists have challenged scholars to move beyond the widely recognised limitations of dominant theorising by taking into account all three perspectives and conceptualising the body as surface, vehicle, and circuit. Because they embrace agnosticism and relational materialism, science and technology studies scholars are in a distinctive position to answer this call. Proponents fully acknowledge the materiality of the body without espousing essentialist claims by effacing the analytic division between agency and structure. Starting from this perspective, I use the concept of corporeal transgression and the phenomenon of phantom limb to reveal how ‘immaterial’– indeed, at times, fictive and fanciful – body parts became socially and materially substantive, engendering transformations within the bodies, minds, and brains of amputees, as well as within the field of neuroscience.