The definition of art is open, subjective, and debatable. There is unanimous agreement among historians, philosophers and artists. Over time there have been many definitions of art, including: "Art is the right ordering of reason '( Thomas Aquinas ), "art is what sets its own rules" ( Schiller ), "the Art is the style "( Max Dvorak ), "art is an expression of society" ( John Ruskin ), "art is the freedom of genius" ( Adolph Loops ), "art is the idea" ( Marcel Duchamp ) "art is the new" ( Jean Dubuffet ), "action art is the life" ( Joseph Beuys ), "Art is whatever men call art" ( Dino Formaggio ). The concept has been changing over time: to the Renaissance, art is only considered the liberal arts; the architecture, the sculpture and painting were "Crafts." Art has always been one of the main means of expression of the human being, through which expresses ideas and feelings, how it relates to the world. Their function can vary from the most practical to ornamental, can have a religious content or simply aesthetic, can be lasting or ephemeral. In the twentieth century is lost even the substrate material: Buys said that life is an art form, highlighting the vital, action. So, everyone is capable of being an artist.