The first stage of meditation is the attempt to keep attention from wandering by tethering it to a fixed idea or a line of ideas. The next stage is its withdrawal from physical surroundings as much as possible. The third is lifting the object of thought to an abstract, non-physical plane, getting absorbed in it. The fourth stage is a turning point. Drop thoughts, rest in mental quiet.
-- Notebooks Category 4: Elementary Meditation > Chapter 1: Preparatory > # 212