But one knows that from outside information rather than from logical inference. In sum, conversion is not legitimate for A propositions. No crows are birds. This result is not a feature of the examples we happened to choose or our having outside information. If all of one group is excluded from another, then obviously all of the other group must equally be excluded from the one.
Conversion is legitimate for E propositions.
As with the E proposition, this is always the case. If some members of one kind of thing are members of another kind then, since the two kinds must have members in common in order for this to be true, some members of the other kind must be members of the first kind. And in order for an I proposition to be false, no members can be common between the two kinds, which will equally make the converse of the original I proposition false. Conversion is legitimate for I propositions. The fact that E and I are symmetrical in distributing or not distributing their terms is significant here.