Studying Kant's Perpetual Peace I happened to notice the concept of adiaphora. Further investigations brought up almost nothing: There are several references to adiaphora in Kant's work that clearly contradict each other.
But that man can be called fantastically virtuous who allows nothing to be morally indifferent (adiaphora) and strews all his steps with duties, as with man-traps; it is not indifferent to him whether I eat meat or fish, drink beer or wine, supposing that both agree with me. Fantastic virtue is a concern with petty details [Mikrologie ] which, were it admit- ted into the doctrine of virtue, would turn the government of virtue into tyranny. (Metaphysics of Morals, The Doctrine of Virtue, XVI)
It is, however, of great consequence to ethics in general to avoid admitting, so long as it is possible, of anything morally intermediate, whether in actions (adiophora) or in human characters; for with such ambiguity all maxims are in danger of forfeiting their precision and stability. Those who are partial to this strict mode of thinking are usually called rigorists (a name which is intended to carry reproach, but which actually praises); their opposites may be called latitudinarians. (Religion within the Limits of Reason Alone, Book I, Observation)
German Wiki on adiaphora is linked to the entry on rigorism which states, quoting the second passage from above, that Kant was rigorous for he didn't admit of anything "morally intermediate". This seems simply impossible, for even in the Perpetual Peace he thinks about what kind of acts are touched by the permissive law, and mentions adiaphora. Another book I consulted on this, unfortunately only available in German, states that the ones denying adiaphora in Kant's philosophy simply mistake "morally intermediate" things for adiaphora, and claims they aren't the same.
Hopefully you can see why I am confused. I think this is a really interesting topic, but I don't know where to look further. I am not asking about the concept of adiaphora here, which, as I am told, is a stoic and later catholic concept, neither am I asking for references in other philosophies - I am solely interested in Kant's understanding of morally indifferent acts. I will be grateful for all kinds of sources and references on-topic.
