Professional accountant Ralph Nelson Elliott fired the opening shot in a decades-long debate when he released The Wave Principle in 1938. His theory of pattern recognition argues that market trends unfold in five waves when traveling in the direction of a primary impulse and 3 waves when opposing that impulse. This theory further stipulates that each wave will subdivide into three waves towards the trend and two against it. Finally, it explains a fractal market in which each wave churns out similar patterns within progressively lower and higher time frames. (For further explanation, see: ​Elliot Wave Theory.)