For qualified persons, and not many are, there is a form of meditational exercise which leads to a certain power over one's dreams and enables the practiser to get into and get out of those dreams. With further knowledge and practice he can even bring a dream under his own control. But not only are certain qualifications of a moral and mental character required of him, he has also to take certain risks which attend this enterprise.

-- Notebooks Category 23: Advanced Contemplation > Chapter 6: Advanced Meditation > # 73