Justice Sotomayor, in construing what is admittedly a confusing and poorly drafted statute, had this to say in DePeirre v. United States about statutory construction:

Of course, this redundancy could have been avoided by simply drafting clause (iii) to penalize offenses involving “a mixture or substance which contains cocaine base,” without reference to clause (ii)—that is, Congress couldhave drafted clause (iii) to specify a separate set of cocaine-related substances, not a subset of those in clause (ii).That we may rue inartful legislative drafting, however,does not excuse us from the responsibility of construing a statute as faithfully as possible to its actual text.11 And as noted earlier, there is no textual support for DePierre’s interpretation of “cocaine base” to mean “crack cocaine.”

We also recognize that our reading of “cocaine” in sub-clause (II) and “cocaine base” in clause (iii) to both refer tochemically basic cocaine is in tension with the usual rule that “when the legislature uses certain language in onepart of the statute and different language in another, the court assumes different meanings were intended.” Sosa v. Alvarez-Machain, 542 U. S. 692, 711, n. 9 (2004) (internal quotation marks omitted). However, because “Congresssometimes uses slightly different language to convey the same message,” Deal v. United States, 508 U. S. 129, 134 (1993) (internal quotation marks omitted), we must be careful not to place too much emphasis on the marginals emantic divergence between the terms “cocaine” and“cocaine base.” As we have already explained, Congresshad good reason to employ the latter term in clause (iii), and the slight inconsistency in nomenclature is insuffi-cient reason to adopt DePierre’s interpretation. Cf. Public Lands Council v. Babbitt, 529 U. S. 728, 746–747 (2000) (suggesting that a “statute’s basic purpose” might supportthe conclusion that “two sets of different words mean the same thing”).

So Canon A says similar words used in different parts of the statute should be interpreted similar. Canon B says Congress may use different language to convey the same message. Got it. \

I feel like re-reading Karl Llewellyn’s Dueling Canons article.