[This statement of the multi-factored approach to deference was written by Stephen Breyer before he became a Justice of the Supreme Court.]

One might try to reconcile this apparently conflicting case law by asking why a court should ever "defer" to an agency's interpretation of the law? After all, judges are charged by statute and Constitution with deciding legal questions. Why should they ever pay particular attention to the agency's legal views?

One can think of two possible jurisprudential answers to these questions. First, one might believe that judges should pay special attention to the agency because the agency knows more about the particular area of the law than does the court. This answer, in part, treats agency lawyers like expert tax lawyers or real estate lawyers to whom judges sometimes listen with particular attention when they must decide a difficult and complex case. In the context of administrative law, this jurisprudential answer may rest upon a particularly important, highly relevant legal fact, namely, the likely intent of the Congress that enacted the statute. The agency that enforces the statute may have had a hand in drafting its provisions. It may possess an internal history in the form of documents or "handed-down oral tradition" that casts light on the meaning of a difficult phrase or provision. Regardless, its staff, in close contact with relevant legislators and staffs, likely understands current congressional views, which, in turn, may, through institutional history, reflect prior understandings. At a minimum, the agency staff understands the sorts of interpretations needed to "make the statute work." It is virtually always proper for a court to assume Congress wanted the statute to work and, at least, did not intend a set of interpretations that would preclude its effective administration.

This "better understanding of congressional will" is reflected in many court statements urging deference. The District of Columbia Circuit, for example, recently wrote:

Courts regard with particular respect the contemporaneous construction of a statute by those initially charged with its enforcement. . . . [W]here the agency was involved in developing the provisions, this principle applies with even greater force.

Similarly, courts have said they find an agency's views more persuasive when they reflect a longstanding, consistent interpretation of the statute. Congress' reenactment of the statute, in the face of an agency interpretation, is also some evidence that the agency's interpretation is correct; at least it suggests that the agency's interpretation does not radically violate current congressional expectations - a fact that, in turn, offers some evidence about the understandings of relevant agency "client groups," providing some (often weak) evidence about the original congressional understanding. There may also be some sense that because of "settled expectations," a statute's words, legally speaking, come to mean what affected parties reasonably understand them to mean over a long period of time, irrespective of a legislature's original understandings. Where all these considerations are absent, for example, where the agency adopts a radically new statutory interpretation, courts have sometimes said that the agency is not entitled to "deference." 

Of course, the strength and the relevance of these considerations varies from case to case. But they all reflect one type of answer to the question "why defer?," namely, "because the agency has a better understanding of relevant law."

A very different sort of answer to the question "why defer?" is, "Congress told the courts to defer in respect to this particular legal question; Congress delegated to the agency the power to decide the relevant question of law." . .

For the most part courts have used "legislative intent to delegate the law-interpreting function" as a kind of legal fiction. They have looked to practical features of the particular circumstances to decide whether it "makes sense," in terms of the need for fair and efficient administration of that statute in light of its substantive purpose, to imply a congressional intent that courts defer to the agency's interpretation. It is nothing new in the law for a court to imagine what a hypothetically "reasonable" legislator would have wanted (given the statute's objective) as an interpretive method of understanding a statutory term surrounded by silence. Nor is it new to answer this question by looking to practical facts surrounding the administration of a statutory scheme. And, there is no reason why one could not apply these general principles, not simply to the question of what a statute's words mean, but also to the question of the extent to which Congress intended that courts should defer to the agency's view of the proper interpretation.

Thus, courts will defer more when the agency has special expertise that it can bring to bear on the legal question. Is the particular question one that the agency or the court is more likely to answer correctly? Does the question, for example, concern common law or constitutional law, or does it concern matters of agency administration? A court may also ask whether the legal question is an important one. Congress is more likely to have focused upon, and answered, major questions, while leaving interstitial matters to answer themselves in the course of the statute's daily administration. A court may also look to see whether the language is "inherently imprecise," i.e., whether the words of the statute are phrased so broadly as to invite agency interpretation. It might also consider the extent to which the answer to the legal question will clarify, illuminate or stabilize a broad area of the law. Finally, a court might ask itself whether the agency can be trusted to give a properly balanced answer. Courts sometimes fear that certain agencies suffer from "tunnel vision" and as a result might seek to expand their power beyond the authority that Congress gave them. Of course, reliance on any or all of these factors as a method of determining a "hypothetical" congressional intent on the "deference" question can quickly be overborne by any tangible evidence of congressional intent, for example, legislative history, suggesting that Congress did resolve, or wanted a court to resolve, the statutory question at issue.

. . .
Using these factors as a means of discerning a hypothetical congressional intent about "deference" has institutional virtues. It allows courts to allocate the law-interpreting function between court and agency in a way likely to work best within any particular statutory scheme. Insofar as Congress is viewed as delegating the power to the agency, it gives the agency flexibility to adapt or to modify past policies.