Modernism is an aesthetic movement functioning in all facets of culture: high art, aesthetic criticism, to mass media, city planning, etc. It is one of many possible reactions to modernity.  In Catholic theology modernism refers to a critique of the absolute rigidity and authoritative nature of the Vatican. Modernist theology challenges the Roman Catholic Institution through Enlightenment reason.  There are four basic aspects to the modernist aesthetic: 1) a belief in progress through technological innovation and rational thought, 2) an opposition to tradition or convention, 3) skepticism, 4) a re-imaging of environment and a willingness to be recreated by it. 
Attempting to gauge the exact birth of modernism is difficult. In terms of European high visual art, it first took shape from approximately 1900-1915. Cubism is an early embodiment of modernism.  Yet it is arguable whether Cubism represents the birth of modern art. The impressionist works of Manet from the mid to late nineteenth century, for example, show strong modernist tendencies.  Clement Greenberg praises Manet's modernist approach to painting, writing, “he saw the problems of painting as first and foremost problems of the medium."  Thus from its beginnings, modernism was essentially focused on form as content.
In the sculptural medium, the assertion of media-specific form is portrayed as aggressive by Robert Morris. He writes, "the concerns of sculpture have been for sometime not only distinct from but hostile to those of painting."  Morris defines sculpture's formal aspects as space, light, and materiality. Sculpture does not create the illusion of tactile reality (as painting does) because it already exists in three dimensions.  When a sculpture is present in a given setting, the juxtaposition of the solid object and empty setting gives a sense of balanced space.  Greenberg claims color for the domain of painting.  Morris agrees color has no place in sculpture. Instead the texture is allowed to reflect light unobstructed by glaring color.  Size Is measured In units of the human scale.  This suggests modernism's reliance on the subject’s gaze.
Modernism is prevalent in philosophy and criticism. For example, Marshall Berman examines Nietzsche's writing,
"Another type of modern throws himself into parodies of the past: he “needs history because it is the storage closet where all the costumes are kept. He notices that none really fit him” -not primitive, not classical not medieval, not Oriental- “so he keeps trying on more and more,” unable to accept the fact that a modern man “can never really look well-dressed,” because no social role in modern times can ever be a perfect fit. Nietzsche’s own stance toward the perils of modernity is to embrace them all with joy: “We moderns, we half-barbarians. We are in the midst of our bliss only when we are most in danger. The only stimulus that tickles us is the infinite, the immeasurable.” 
This shows the self-reflection of modernist thought, seen clearly in the fact that the subject of these passages, and Berman’s piece as a whole, is the author himself. We also can see the need to be made over in Nietzsche’s disconnect of the individual from society. This concepts is visualized through the action of trying on costumes, like masks, in that the subject is constantly tearing off one identity and taking on another, and that he is aware of the falsity in all of these culture constructs of himself.
Some theorists point to the rise of postmodernism as proof of the death of the modernist movement. Or perhaps modernism has become the new conservative convention to be fought against.  Yet others see postmodernism as less of a new form and more of a reaction- often pessimistic- to the convictions of modernism. 
Though much of the idea of modernism relates to high art and criticism, modernism is all around us, in nearly every medium that we interact with. One such example could be Jones Beach, NY, which may at first be considered the near natural unmediated medium of the ‘Beach’ and yet an unmistakably modernist invention. Other examples of non-high art mediums where modernism is present are Time Square, or Baudelaire’s Paris Spleen. Thus modernism is represented in all forms of media.
The aesthetics of modernism attempt to breakdown the traditional, classical way of representing nature.  In traditional European conventions, the artist attempts to represent nature perfectly. Mastery comes when one can limit the viewers awareness that the image they are looking at is mediated, thus attempting to eviscerate the medium from the message. Greenberg writes, "The medium was regrettable if necessary physical obstacle between the artist and his audience."  Conversely, modernism sees the limiting nature of a given medium as, paradoxically, enabling a dialogue between the content and its form. In doing this, modernism is self-consciously aware of its medium. In reference to Clement Greenberg, and apparently McLuhan, Marshal Berman writes, "...the only legitimate concern of modernist art was art itself; furthermore, the only rightful focus for an artist in any given form or genre was the nature and limits of the genre: the medium is the message... Modernism, then, was the quest for the pure, self-referential art object."  Modern art engages in cultural criticism just by being apprehended.