Drawing is the basis.
Often necessary to « note » an idea of a sculpture or to make progress when researching a form, it stays nonetheless self-sufficient in many cases. As a work of art in itself, it can be made with pencil, charcoal, ink, even wash drawing…
Other techniques like collages or assemblages are useful to the sculptor’s hand who « naturally » needs to use a bit of volume to the two dimensions.
Most likely because of the spontaneity involved, these activities not only allow a vast freedom in associating materials but also are done with an almost childish joy of blending everything together. This creative space de facto abolishes strict categories : drawings, scuptures, collages, assemblages, much to the delight of the maker.