Sellars has two good ideas associated with material inference:
There are some inferences that are good, not in virtue of their logical form.
Turn the above thought on its head and say: we can understand the content of these descriptive terms in terms of the materially good inferences they appear in (as premises or conclusions).
By this account, material proprieties of inference are more fundamental than / conceptually prior to logical validity. You have to start with the notion of a good inference in order to understand what a logically good inference is.