According to Levin and Rappaport, the property, deletion (suppression) of external argument, follows from the fact that the adjectival passive participle is created from the verbal passive participle, which involves suppression of external argument, and the property, externalization of an argument, is a consequence of the category change; a general property of adjectives is that they require external argument.
properties other than the category conversion do not need to be stipulated in APF, according to Levin and Rappaport.