The practice of understanding by making marks is common to the disciplines of anthropology, fine art and architecture.  This thesis holds that the written word is not the only means by which theory can be produced.  Indeed, it is appropriate to the theorising of fields such as architecture and art that it should use the tools of the discipline at hand.  In this thesis I demonstrate that this is so, by way of a series of drawing projects and experiments in notation.  Sometimes a drawing might illustrate or elaborate an argument established in the text, or vice-versa.  Three key inscriptive practices are identified: notation, drawing and diagrams. The prevalence of inscriptive practices in modern Western societies allows them to become deeply ingrained as ways of thinking.  This brings me to the second component in the title of the thesis, namely the idea of the ‘thinking tool.’ By that I mean the manner in which a set of codes for drawing becomes a way of organising and understanding phenomena.  For example, an architect’s section drawing becomes a tool by which volume can be explored, whilst the plan drawing is a tool for understanding spatial relations on a more organisational level. Key to this is an understanding of Bergson’s notion of duration and Deleuze’s work on locating the diagram within the paintings of Francis Bacon. The inscriptive practice is not primarily a form of representation or mimesis, but rather a way of articulating the world, not an expression of a pre-existing thought, but a thought process in itself.  As such, the actual practice of making the mark is of utmost importance anthropologically, as it is the way in which the mark is made that organises our thoughts rather than the completed artefact.