This chapter introduces the foundational principles of oblique axonometric projection, establishing its relationship to orthogonal axonometry while emphasizing its autonomy as a complete system of representation. The theoretical framework is developed through spatial reasoning, without reliance on imagery, guiding the reader to a deeper conceptual understanding of projection geometry. Definitions of spatial elements and their infinite and relative properties are explored, preparing the reader for the practical and intellectual challenges of oblique drawing. The aim is to develop conscious, methodical control of geometric representation, overcoming intuitive but imprecise approaches to descriptive geometry.