Blurriness -- in the sense of blurred realities --- is in opposition  to the clear,  distinct   pictures of reality that emphasis clarity. 

For instance, Wittgenstein  in the Tractatus Logico-Philosophicus  appeals to clarity when he  characterises the aim, task and results of philosophy. The task for philosophy is to make thoughts clear; whilst making a thought clear is making clear a picture of reality. 

Analogue photography's representations were traditionally seen capturing  a slice of real life in terms of the conventions of   clarity  and sharpness.  Photographic realism was interpreted as faithfully representing  the reality of the material world--a framed, cut-out of reality.  Representing was understood in terms of   clarity  with clarity  interpreted as depicting  (abbilden in Wittgenstein) which was then interpreted as mirroring  or copying. Photographic theory from Bazin, Benjamin, Barthes, Berger, Sjarkowski, up until the mid-1970s was in general preoccupied with the documentary and the vernacular. 

 In contrast, Claude  Monet's Water Lilies have a blurry, out-of-focus effect that characterises the wide stretches of water. This aspect of Monet’s later work was an actual aesthetic choice, and rather than being a loss of distinctiveness, the indistinct   can be interpreted in terms of the aesthetic category of blurriness. Blurriness as an out of focus aesthetic is associated with the transitory, contingency,  disorder, movement, incompleteness, ambiguity, the indeterminate, the indistinct, the poetic, the formless. 

A way into  the formless in art is   Georges Bataille’s concept of l’informe  speaks to what is settled, denigrated, repressed. This the modernist  emphasis on significant-form denigrates the formless as the low, the base and represses it. Yve-Alain Bois and Rosalind Krauss in their   Formless: A User's Guide  (exhibition and catalogue, 1996) used the   informe   to "shake" the high modernist art world of the 20th century  with its traditional formalist  art history of Greenberg by negotiating the return of its own long-repressed, long-denied "other." Their argument is that the informe, must become "operational," i.e., be "put to use."  There is a    discussion   about this from various perspectives at November.

Blurred realities is not the breakup of traditional forms and values per se, as we have the opposition of   formed vs. formless with the formed being placed in the subordinate position. The formless is not simply the lack of form since visual art is giving form to contingent material.  So form and formless are put into play in a movement. 

In this context an example of what is shaken up and dislodged by this movement of contradictions is the clarity of  form in the classical or Aristotelian sense of an artefact reposing in the unity, integrity, and harmony of its disparate elements. It is the break of that unity, the resistance of the material to integration into a totality --- the autonomy of the parts with respect to the whole -- that sets the new modernist work apart from the old classics of tradition. 

Blurriness negates clarity and formalism without  embracing the ongoing progressive innovation (the new) driven by subjectivity or pastiche.

Update

A contemporary example of blurred pictures is Gerhard Richter's series of blurred photo-paintings. Manet was before modernist abstraction whilst Richter was after and his subjects range from portraits, furniture, landscapes, fighter jets to scenes from Nazi history.  Richter transforms a photograph into a photo-painting and then mechanically blurs the oil painted image with a squeegee passed across it.

Richter's photo-paintings used  photographs as the source, basis, or subject of paintings and they are paintings of photographs that make the paintings a doubly distanced reference to  the  object or scene,  an affirmation of photography by painting and an affirmation of painting in the face of photography.  The softening blurring  in these photo paintings paradoxically reproducing photographic effects -- creating the photographic effect of an out-of-focus image --- while simultaneously revealing his painterly hand.

Blurring refers to the general idea of vagueness, indecisiveness, anti-definition.