"The principal defect of all materialism up to now … is that the external object, reality, the sensible world, is grasped in the form of an object of an intuition; but not as a concrete human activity, as practice, in a subjective way. This is why the active aspect was developed by idealism, in opposition to materialism — but only in an abstract way, since idealism naturally does not know real concrete activity as such."
— Karl Marx, Theses on Feuerbach
"I have been a selfish being all my life, in practice, though not in principle."
— Jane Austen, Pride and Prejudice
In a general sense, the word "practice" elides between action and state of being. For instance, the OED defines the noun "practice" as: "The habitual doing or carrying out of something, usual or customary action or performance, action as opposed to profession, theory, knowledge, etc. ... A custom; a habit; a habitual action." As a verb, the OED defines "practice" as "Repeated exercise in or performance of an activity so as to acquire or maintain proficiency in it; activity undertaken to this end. ... The action of doing something; performance, operation; method of action or working. ... An action, a deed; in plural, doings, proceedings." 
Practice is where the dialectic between thought and action plays out. In the Symposium, Plato says, "And the true nature of going, or being led by another, to the things of love, is to begin from the beauties of earth and mount upwards for the sake of that other beauty, using these steps only, and from one going on to two, and from two to all fair forms to fair practices, and from fair practices to fair notions, until from fair notions he arrives at the notion of absolute beauty, and at last knows what the essence of beauty is." Here, practice mediates between two different, seemingly opposed realms: Practice is a necessary step on the path leading from objects in the world to ideas -- the only way to reach the idea(l) of absolute beauty. Interestingly, in Plato's paradigm, the path leads from the physical world to abstraction, while typically practice is thought to be the implementation, the practical embodiment, of theoretical, or abstract, concepts -- thus reversing this order.
For instance, the OED also defines "practice" as "the practical aspect or application of something as opposed to theoretical aspect. ... In Marxism, the social activity which should result from and complement the theory of Communism."  In fact, according to Catherine Bell,  current uses of the term "practice" or "practices" in social and cultural anthropology originate with Karl Marx. She notes multiple, sometimes contradictory uses and definitions of "practice" arising in cultural and anthropological theory as a result of Marx's "flexible" use of the term. Notably, he used the word both descriptively and prescriptively. In a descriptive sense, Marx sees practice as practical activity. "In this framework, practice mediates or reintegrates subject and object (consciousness and reality), which is to say that these polarized constructs are thought to exist only as they exist in and through practice."  In a prescriptive sense, Marx thought practice should test theory while simultaneously providing data for new theory. "This dialectical unity of theory and practice was meant to indict the inadequacy of abstract thinking, knowledge and truth. At the same time, it gave theory an important place in the practice of political activity."  Marx considered the practice of the class struggle to be fertilized by theory.
In analyzing practice as a way of approaching notions of ritual, Bell sees practice as "inherently strategic, manipulative and expedient,"  constantly changing and improvising in response to particular situations. She notes that according to Pierre Bourdieu, the contexts of particular practices are usually ambiguous and indeterminate rather than clear and definite.
Bourdieu relates practice to his idea of the "habitus," "the principle by which individual and collective practices are produced and the matrix in which objective structures are realized within the (subjective) dispositions that produce practices."  Habitus to some extent internalize objective structures and rules. Bourdieu believes that the principles behind practices are often hidden from those who practice them, so that questioning practitioners about the reasons for their practices is not particularly useful. "The explanation agents may provide of their own practice, conceals, even from their own eyes, the true nature of their practical mastery, i.e., that it is learned ignorance, a mode of practical knowledge not comprising knowledge of its own principles."  He notes that the "order of practice tends to naturalize its own arbitrariness" by a system of classification that reinforces symbolic power relations. 
Louis Althusser further suggests that to understand a particular practice it is necessary to question the practice's relationship to its object or intent. It is important to look at what a practice sees itself doing -- and what it doesn't see. Bell notes that, according to Althusser, practice's lack of ability to see what it is really doing lies in a misunderstanding. "Why is practice blind to what it produces? Because it is still fixed on the old question, the old horizon, on which the new problem is not visible."  Thus, in his view, practices are engaged in a continual transformation of the context in which they exist in order to generate new problems.
Raymond Williams considers the relationship between social or cultural practices and the media in which they are manifest. He notes that mediation usually denotes "an activity: an active relationship or, more interestingly, a specific transformation of material."  This idea of transformation via specific media echoes and relates to Althusser's point that practices are continually "transforming" the situations in which they operate.
Williams discusses the change from use of the word "medium" to use of the word "practice" in an art historical context. He notes that the word "medium" in relation to paint originally meant the liquid with which pigments are mixed to produce paint itself. The meaning of medium "was then extended to the active mixture and so to the specific practice."  But he also points out that interpreting the medium's properties as defining the entire practice "then suppressed the full sense of practice, which has always to be defined as work on a material for a specific purpose within certain necessary social conditions."  Williams traces the history of art making as it relates to work within capitalist production. Ultimately art and knowledge became commodities -- like any other product, for sale. As industrial workers become alienated from their own labor and what they produced, art as skill or craft was idealized. The material objects artists produced began to take on the higher, displaced meaning and significance "of work -- that of using human energy on material for an autonomous purpose."  This idealization of art as well as the perception of art as defined by its medium (such as painting or sculpture) would have been threatened if art had been seen, rather, as "a particular case of conscious practice." 
Changing technologies have generated the need for artists and writers to develop new skills and techniques. Williams points out that "A new technique has often been seen ... as a new relationship, or as depending on a new relationship. Thus what had been isolated as a medium, in many ways rightly as a way of emphasizing the material production which any art must be, came to be seen, inevitably, as social practice."  Art making thus becomes a practice. Rather than focusing on a particular medium, art as practice incorporates cultural, political, aesthetic, social and economic dimensions. It involves a systematic, methodological set of strategies that imply an ideological stance incorporating literary theory, feminist, art, scientific, psychoanalytic, linguistic, anthropological sources.
This notion of art as practice was influenced by the rise of conceptual art in the early sixties, with its political overtones and close ties to the history of the avant-garde (e.g., Dadaism, Surrealism, as Hal Foster points out in The Return of the Real). In this light, art making becomes process- rather than object-based. Marxist, structuralist, anthropological and semiotic thought now permeate what had been defined as a strictly material realm. The requisite academic training for artists has taken on theoretical rather than practical aspects. An artist engaged in a practice is conscious of the many social dimensions of his or her activity, which ostensibly bridges gaps between, artistic, curatorial, critical, research and conceptual study. It is temporal, experiential and contextual rather than medium-specific.
But what are the power relationships and principles that current art practice reinforces? If practice becomes an end in itself, does its role as mediator become obsolete, eventually eliminating the need (or desire) for its product? According to the OED, practice has an archaic meaning: "The action of scheming or planning, especially in an underhand or evil way; treachery; trickery, artifice, deception. ... Dealings, negotiation; especially underhand dealings, intrigue. ... A scheme, a conspiracy; an artifice, a trick." 
Art as practice at first appears to demythologize and demystify the process of art making. But every practice is also a closed, private society. Perhaps "art practice" undermines its own demystification, simply inventing fetishism of art in a new guise. Certainly, when we view art as a practice, we are also mystifying and exalting it as a specialization requiring prescribed initiation into its secret, esoteric rites. So perhaps practice's old problems and horizons remain intact.
Committee on the Visual Arts