Kolb integrated this learning cycle with a theory of learning styles, wherein each style prefers two of the four parts of the cycle. The cycle is quadrisected by a horizontal and vertical axis. The vertical axis represents how knowledge can be grasped, through "concrete experience" or through "abstract conceptualization", or by a combination of both. The horizontal axis represents how knowledge is transformed or constructed through "reflective observation" or "active experimentation". These two axes form the four quadrants that can be seen as four stages: concrete experience (CE), reflective observation (RO), abstract conceptualization (AC) and active experimentation (AE) and as four styles of learning: diverging, assimilating, converging and accommodating. The concept of learning styles has been criticised, see .