reason for being; raison d'être
rationalization; justification
ostensible (surface) reason
rationalization; justification
ratio decidendi; reason for a verdict
principle of sufficient reason (logic)
statement of purpose; essay/letter in university application form
principle of reason (logic)
the reason(s) is (are) as follows
invitation letter (e.g. document in support of a visa to enter Japan)
reason for revision; reason for modification
invitation letter (e.g. document in support of a visa to enter Japan)