Favor libertatis : A Peculiar Institution. On Marcell. Digest 28,4,3 pr. -1. In a case of the imperial cognitio reported by the jurist Marcellus the testator had erased the heirs from the testament. He had also erased a disposal of freedom for a slave. The question arose whether the whole testament - which also contained legacies - was invalid because it lacked the institution of an heir or whether the legacies and the disposal of freedom should be considered legally valid. In Marcellus' opinion the legacies should be considered legally valid, this being not only the most benign but also the most cautious solution to the problem. The emperor Marcus Aurelius decides in the latter sense being convinced that the testator wanted to keep up the legacies. This is quite a revolutionary decision in so far as it overrides the dogma of Roman jurisprudence nemo pro parte testatus, pro parte intestatus decedere potest. But the real punch line of the text is hidden in the paragraph 1 which erroneously has been considered to be a separate case. The principle behind the emperor's decision concerning the legacies is that everything should be done by the law to realize the testator's will. From this perspective it would be obvious that the disposal for freedom should be void since the testator had erased it. Marcus Aurelius does not obey to this logic but to Marcellus' appeal to his humanity. The ultimate reason for this behavior is the favor libertatis, a guideline for Roman jurisprudence which though well known has never been the object of a thorough analysis.