This is the unifying principle proposed by H.C. Rajpoot, for finding out the solid angle subtended by any polygonal plane at any point in the space. It gives the simplest, easiest & the most versatile methods for calculating the mathematically correct value of solid angle subtended by any plane bounded by the straight lines like triangle, quadrilateral like rectangle, square, rhombus, trapezium etc., any regular or irregular polygon like pentagon, hexagon, heptagon, octagon etc.) at any point in the space. This theory requires only one standard formula to calculate solid angle subtended by any polygon. It is the unifying principle applied for any polygon.