In his 1961 essay "Concept Art", Henry Flynt wrote
Concept art is first of all an art of which the material is concepts, as the material of e.g. music is sound. Since concepts are closely bound up with language, concept art is a kind of art of which the material is language.
A work like Robert Rauschenberg's portrait of Iris Clert, a telegram sent to her gallery simply saying "This is a portrait of Iris Clert if I say so" seems to be entirely captured by a description (although some may argue that it is somehow incomplete without the artifact of the telegram itself). Does this mean that it is inherently sufficient to provide a description of a conceptual art in place of the work itself? This would certainly simplify the task of making these works accessible. It is however dangerous to make these sorts of generalizations. Many artists considered "Conceptual" artists would not describe themselves that way and may have a different read on what is meant by conceptual art"
Sol Lewitt put it this way in 1967:
In conceptual art the idea or concept is the most important aspect of the work. When an artist uses a conceptual form of art, it means that all of the planning and decisions are made beforehand and the execution is a perfunctory affair. The idea becomes the machine that makes the art. (full text)
In Lewitt's statement the emphasis has shifted. The work in this case is a sort of system by which something is done or created. The idea leads inexorably to the artwork, without consideration for how it might look, but the concept is understood by the viewer through perception of the finished work (which he defines to mean "the apprehension of the sense data, the objective understanding of the idea, and simultaneously a subjective interpretation of both"). For Lewitt, it seems the rigorous pursuit of a concept was his way of producing a significant object. A description would not suffice.
Many conceptual works are texts, such as Lawrence Weiner's text pieces, and as such, essentially serve as their own accessible description. Although he takes care in how the texts are presented, he has stated about these pieces that "Once you know about a work of mine you own it. There's no way I can climb inside someone's head and remove it." Jenny Holzer's work is usually entirely textual as well, with the text presented in projections, in posters and on scrolling LED signs, but it is hard to ignore the importance of context and the experiential impact of a work like "Untitled"
Some of Lawrence Weiner's texts are simple, evocative instructions describing an action to be performed. Yoko Ono produced "Grapefruit", a book of instructions for the creation of possible works of art. The artist Erwin Wurm has created sets of instructions for the audience to follow in order to create temporary sculptures using their own bodies and everyday objects. These are examples of what is sometimes called Heuristic Art. The instructions have something in common with a script or musical score, but since the primary experience of the work is in reading and following the instructions, the piece is fully contained in the text until the reader reads or hears it. The reader may be incapable of performing the actions, but they are almost certainly able to understand the instructions. The audience is one and the same with the interpreter. Scores and scripts, on the other hand, are generally 'interpreted' by performers for the benefit of the audience, meaning that the 'work' has two stages of manifestation: as score and as performance. I will look more deeply into this later.