I have previously said that the Administrative Procedure Act ("APA") distinction between legislative and interpretive regulations does not address deference. I did, however, address both the APA and deference in my article, Townsend, John A., The Report of the Death of the Interpretive Regulation Is an Exaggeration (August 23, 2020). Available at SSRN: https://ssrn.com/abstract=3400489. But, I did not tie the two together as crisply as I should have.
I recently realized, although they are different “regimes” – APA (including the legislative / interpretive regulation divide in the APA) and deference – they do address the same issue in the same way. Indeed, the APA distinction between legislative and interpretive regulations was based on a similar distinction that applied to under pre-APA law for deference to agency interpretations and the related concept of retroactive application of agency interpretations (generally retroactivity the norm for interpretive regulations and generally prospectivity the norm for legislative regulations).
Before and after the APA, the distinguishing difference between legislative and interpretive regulations is: (i) the legislative regulation based on express authority to create the law (create a new obligation or right) is the law, with necessarily the force of law (example, § 1502 for consolidated return regulations); and (ii) the interpretive regulations based on express or implied authority to interpret otherwise ambiguous statutory text within the scope of the ambiguity, but does not add any new right or obligation within the scope of the statutory text (example § 162's away from home statutory text addressed in United States v. Correll, 389 U.S. 299 (1967)). That was true before the APA, so when Congress used the APA used the legislative / interpretive concepts (called interpretative in the APA), that was the background that defined those terms in the APA and informed both Congress and original public readers of the APA as to their meanings.
What that means is that, if a regulations interpretation is entitled to deference, now called Chevron deference (as a reasonable interpretation within the scope of ambiguity in statutory text), the regulation is an interpretive regulation rather than a legislative regulation for both APA purposes and for deference. Simply because a court defers to an agency regulations interpretation does not mean that the regulations interpretation has been magically transformed into a legislative regulation. (Courts do sometimes state that deferring to a reasonable agency interpretation (say Chevron Step Two) gives the interpretation the force of law, a distinguishing characteristic of a legislative regulation; I do address that misunderstanding in some detail in the article, but bottom-line, force of law is a consequence of a legislative regulation after it is determined to be a legislative regulation rather than a test of whether the regulation is legislative to start with.)
As I reflect on it, sometimes the simplest explanation is the best explanation. That is a variation of Occam’s Razor (with Occam variously spelled and sometimes called the law of parsimony). See Wikipedia Enter, Occam’s Razor, here (noting that it is variously paraphrased by statements like "the simplest explanation is most likely the right one").
I will likely revise my article above to correct some
errors, add some nuance, and incorporate this simpler explanation.