LeWitt's conceptual pieces often did take on at least basic material form, although not necessarily at his own hands. In the spirit of the medieval workshop in which the master conceives of a work and apprentices carry out his instructions based on preliminary drawings, LeWitt would provide an assistant or a group of assistants with directions for producing a work of art. Instructions for these works, whether large-scale wall drawings or outdoor sculptures, were deliberately vague so that the end result was not completely controlled by the artist that conceived the work. In this way, LeWitt challenged some very fundamental beliefs about art, including the authority of the artist in the production of a work. His emphasis is most often on process and materials (or the lack thereof in the case of the latter) rather than on imbuing a work with a specific message or narrative. Art, for LeWitt, could exist for its own sake. Meaning was not a requirement.