  The key to escape from this cycle is said to lie in realization of the truth about sentient existence—that it is characterized by suffering, impermanence and non-self. But this realization is not easily achieved, since acts of appropriation have already made desire, aversion and ignorance deeply entrenched habits of mind. Thus the measures specified in (4) include various forms of training designed to replace such habits with others that are more conducive to seeing things as they are. Training in meditation is also prescribed, as a way of enhancing one’s observational abilities, especially with respect to one’s own psychological states. Insight is cultivated through the use of these newly developed observational powers, as informed by knowledge acquired through the exercise of philosophical rationality. There is a debate in the later tradition as to whether final release can be attained through theoretical insight alone, through meditation alone, or only by using both techniques. Ch’an, for instance, is based on the premise that enlightenment can be attained through meditation alone, whereas Theravāda advocates using both but also holds that analysis alone may be sufficient for some. (This disagreement begins with a dispute over how to interpret D I.77–84.) The third option seems the most plausible, but the first is certainly of some interest given its suggestion that one can attain the ideal state for humans just by doing philosophy.