Reading with Gilles Deleuze, this thesis explores art as a production that abandons representation as a formation of identity in favour of an ontology of becoming. I argue that the move to abstraction in painting resonates with the aim of "thought without image" because it counters representation with a radical materiality that returns painting to the movement of matter. In order to situate Deleuze's thinking on art within a trajectory of a philosophy of becoming I open the thesis with a chapter on Bergson and Merleau-Ponty. Here I introduce the notion of 'thinking in painting' and argue that, while in Merleau-Ponty's phenomenology of art painting is a pedagogical investigation of the pre-human, chaotic and invisible 'depth' of a lived visible world, Deleuze takes Bergson's commitment to the possibility of moving beyond the human seriously and reverses the order of perception in order to seize the non-human virtual that eludes actualization. For Deleuze, the task of painting is therefore not to reveal the ontogenesis of the actual and the lived, but to extract the virtual and to embody it as a monument to that event. In abstraction the interest moves from the mechanism of perception to the work of paint, and in the subsequent chapters on Mondrian, Pollock, Klee and Bacon I explore specific practices and their peculiar logic of sensation. In Mondrian we see the strange space of virtuality unleashed when the line is not constrained by the closure of the punctual system, and in Pollock's explosive "all-over" paintings identify that space not as a chaos but as a chaosmosis or machinic heterogeneity. I argue that by understanding these modulating and rhythmic compositions as haptic spaces, we break through the distancing of visibility and can begin to think at the level of expressive matter. I then turn to Klee, and using the famous image of "taking a walk with a line" explore the notion of the emergent figure in the context of Klee's aim to "render visible". What we find is an art where space and the form of expression works on the plane of composition and refers only to the unfolding rhythms of the abstract line. In the final chapter I discuss Bacon's portraits and look at how the multiplicity of the event that is maintained in the diagrammatic composition is drawn into the recognizable face. I conclude that the embodiment of the non-human event forces thought to confront the possibility of the emergent identity that is realized in the abstraction of "thinking in painting".