The tautology is the conceptual equivalent of the monochrome. It is the proposition which is necessarily true; stating its truth thus conveys no information. (In Kantian terms: a tautology expresses an analytic judgment.) Prototypical tautologies are the truths of logic and mathematics.
A circular statement may be tautological in that its very form guarantees its truth. Joseph Kosuth has presented many such statements as visual artworks – e.g., the self-referential neon pieces and the "Nine Paintings with Words as Art" displayed above.
Definitions are often viewed as tautological propositions, although it would be more precise to say that they aren't propositions at all: they are stipulative acts of language construction. Kosuth has presented many definitions as artworks (in the series "One and Three Things", and "Titled (Art as Idea as Idea)"). Note, however, that these series also include entries from etymological dictionaries and translation dictionaries, whose philosophical status is rather different.
Kosuth has claimed that all artworks are tautologies. This idea is based on a supposed analogy between the realm of art and the realm of mathematics – where mathematics is construed as the construction and exploration of axiomatic systems.
We see now that the axioms of a geometry are simply definitions, and that the theorems of a geometry are simply the logical consequences of these definitions. A geometry is not in itself about physical space; in itself it cannot be said to be 'about' anything. (...) All that the geometry itself tells us is that if anything can be brought under the definitions, it will also satisfy the theorems. It is therefore a purely logical system, and its propositions are purely analytic propositions.
Alfred J. Ayer: Language, Truth and Logic. 1936.
[p. 78 of the second edition (London: V. Gollancz, 1946)]
Quoted in: Joseph Kosuth: "Art after Philosophy, Part I",
Studio International, October 1969, pp. 134-137.

The propositions of philosophy are not factual, but linguistic in character [...]; they express definitions, or the formal consequences of definitions. Accordingly, we may say that philosophy is a department of logic. For we shall see that the characteristic mark of a purely logical inquiry is that it is concerned with the formal consequences of our definitions and not with questions of empirical fact.
Alfred J. Ayer: Language, Truth and Logic. 1936.
[p. 44 of the second edition (London: V. Gollancz, 1946)]

Works of art are analytic propositions. That is, viewed within their context – as art – they provide no information what-so-ever about any matter of fact. A work of art is a tautology in that it is a presentation of the artist's intention, that is, he is saying that that particular work of art is art, which means, is a definition of art. Thus, that it is art is true a priori (which is what Judd means when he states that "if someone calls it art, it's art").
Joseph Kosuth: "Art after Philosophy, Part I",
Studio International, October 1969, pp. 134-137.
Exercises

(1) Kosuth's pronouncement implies that all artworks are equivalent in their meaninglessness. This contradicts our experience. It also contradicts Kosuth's art practice, and his other writings. Analyse the flaw in Kosuth's argument. (Hint: Take into account the theory of Speech Acts.)]
(2) Kosuth assumes an analogy between the practice of art and the practice of mathematics, but does not elaborate this idea in any detail.Do this, and report on your findings.

Joseph Kosuth's Tautologies
···