Full Idea
'All crows are black' cannot say quite the same as 'All non-black things are non-crows', for the two are confirmed by different evidence. Subject matter looks to be the distinguishing feature. One is about crows, the other not.
Gist of Idea
If sentences point to different evidence, they must have different subject-matter
Source
Stephen Yablo (Aboutness [2014], Intro)
Book Reference
Yablo,Stephen: 'Aboutness' [Princeton 2014], p.2
A Reaction
You might reply that they are confirmed by the same evidence (but only in its unobtainable totality). The point, I think, is that the sentences invite you to start your search in different places.