opinion: Mr. Justice Murphy
  delivered the opinion of the Court.
  This case is here for the second time. In S. E. C. v. Chenery Corp., 318 U. S. 80, we held that an order of the Securities and Exchange Commission could not be sustained on the grounds upon which that agency acted. We therefore directed that the case be remanded to the Commission for such further proceedings as might be appropriate. On remand, the Commission reexamined the problem, recast its rationale and reached the same result. The issue now is whether the Commission’s action is proper in light of the principles established in our prior decision.
  When the case was first here, we emphasized a simple but fundamental rule of administrative law. That rule is to the effect that a reviewing court, in dealing with a determination or judgment which an administrative agency alone is authorized to make, must judge the propriety of such action solely by the grounds invoked by the agency. If those grounds are inadequate or improper, the court is powerless to affirm the administrative action by substituting what it considers to be a more adequate or proper basis. To do so would propel the court into the domain which Congress has set aside exclusively for the administrative agency.
  We also emphasized in our prior decision an important corollary of the foregoing rule. If the administrative action is to be tested by the basis upon which it purports to rest, that basis must be set forth with such clarity as to be understandable. It will not do for a court to be compelled to guess at the theory underlying the agency’s action; nor can a court be expected' to chisel that which must be precise from what the agency has left vague and indecisive. In other words, “We must know what a decision means before the duty becomes ours to say whether it is right or wrong.” United States v. Chicago, M., St. P. & P.R. Co., 294 U.S. 499, 511.
  Applying this rule and its corollary, the Court was unable to sustain the Commission’s original action. The Commission had been dealing with the reorganization of the Federal Water Service Corporation (Federal), a holding company registered under the Public Utility Holding Company Act of 1935, 49 Stat. 803. During the period when successive reorganization plans proposed by the management were before the Commission, the officers, directors and controlling stockholders of Federal purchased a substantial amount of Federal’s preferred stock on the over-the-counter market. Under the fourth reorganization plan, this preferred stock was to be converted into common stock of a new corporation; on the basis of the purchases of preferred stock, the management would have received more than 10% of this new common stock. It was frankly admitted that the management’s purpose in buying the preferred stock was to protect its interest in the new company. It was also plain that there was no fraud or lack of disclosure in making these purchases.
  But the Commission would not approve the fourth plan so long as the preferred stock purchased by the management was to be treated on a parity with the other preferred stock. It felt that the officers and directors of a holding company in process of reorganization under the Act were fiduciaries and were under a duty not to trade in the securities of that company during the reorganization period. 8 S. E. C. 893, 915-921. And so the plan was amended to provide that the preferred stock acquired by the management, unlike that held by others, was not to be converted into the new common stock; instead, it was to be surrendered at cost plus dividends accumulated since the purchase dates. As amended, the plan was approved by the Commission over the management’s objections. 10 S. E. C. 200.
  The Court interpreted the Commission’s order approving this amended plan as grounded solely upon judicial authority. The Commission appeared to have treated the preferred stock acquired by the management in accordance with what it thought were standards theretofore recognized by courts. If it intended to create new standards growing out of its experience in effectuating the legislative policy, it failed to express itself with sufficient clarity and precision to be so understood. Hence the order was judged by the only standards clearly invoked by the Commission. On that basis, the order could not stand. The opinion pointed out that courts do not impose upon officers and directors of a corporation any fiduciary duty to its stockholders which precludes them, merely because they are officers and directors, from buying and selling the corporation’s stock. Nor was it felt that the cases upon which the Commission relied established any principles of law or equity which in themselves would be sufficient to justify this order.
  The opinion further noted that neither Congress nor the Commission had promulgated any general rule proscribing such action as the purchase of preferred stock by Federal’s management. And the only judge-made rule of equity which might have justified the Commission’s order related to fraud or mismanagement of the reorganization by the officers and directors, matters which were admittedly absent in this situation.
  After the case was remanded to the Commission, Federal Water and Gas Corp. (Federal Water), the surviving corporation under the reorganization plan, made an application for approval of an amendment to the plan to provide for the issuance of new common stock of the reorganized company. This stock was to be distributed to the members of Federal’s management on the basis of the shares of the old preferred stock which they had acquired during the period of reorganization, thereby placing them in the same position as the public holders of the old preferred stock. The intervening members of Federal’s management joined in this request. The Commission denied the application in an order issued on February 8,1945. Holding Company Act Release No. 5584. That order was reversed by the Court of Appeals, 80 U. S. App. D. C. 365, 154 F. 2d 6, which felt that our prior decision precluded such action by the Commission.
  The latest order of the Commission definitely avoids the fatal error of relying on judicial precedents which do not sustain it. This time, after a thorough reexamination of the problem in light of the purposes and standards of the Holding Company Act, the Commission has concluded that the proposed transaction is inconsistent with the standards of §§ 7 and 11 of the Act. It has drawn heavily upon its accumulated experience in dealing with utility reorganizations. And it has expressed its reasons with a clarity and thoroughness that admit of no doubt as to the underlying basis of its order.
  The argument is pressed upon us, however, that the Commission was foreclosed from taking such a step following our prior decision. It is said that, in the absence of findings of conscious wrongdoing on the part of Federal’s management, the Commission could not determine by an order in this particular case that it was inconsistent with the statutory standards to permit Federal’s management to realize a profit through the reorganization purchases. All that it could do was to enter an order allowing an amendment to the plan so that the proposed transaction could be consummated. Under this view, the Commission would be free only to promulgate a general rule outlawing such profits in future utility reorganizations; but such a rule would have to be prospective in nature and have no retroactive effect upon the instant situation.
  We reject this contention, for it grows out of a misapprehension of our prior decision and of the Commission’s statutory duties. We held no more and no less than that the Commission’s first order was unsupportable for the reasons supplied by that agency. But when the case left this Court, the problem whether Federal’s management should be treated equally with other preferred stockholders still lacked a final and complete answer. It was clear that the Commission could not give a negative answer by resort to prior judicial declarations. And it was also clear that the Commission was not bound by settled judicial precedents in a situation of this nature. 318 U. S. at 89. Still unsettled, however, was the answer the Commission might give were it to bring to bear on the facts the proper administrative and statutory considerations, a function which belongs exclusively to the Commission in the first instance. The administrative process had taken an erroneous rather than a final turn. Hence we carefully refrained from expressing any views as to the propriety of an order rooted in the proper and relevant considerations. See Siegel Co. v. Federal Trade Commission, 327 U. S. 608, 613-614.
  When the case was directed to be remanded to the Commission for such further proceedings as might be appropriate, it was with the thought that the Commission would give full effect to its duties in harmony with the views we had expressed. Ford Motor Co. v. Labor Board, 305 U. S. 364, 374; Federal Radio Commission v. Nelson Bros. Co., 289 U. S. 266, 278. This obviously meant something more than the entry of a perfunctory order giving parity treatment to the management holdings of preferred stock. The fact that the Commission had committed a legal error in its first disposition of the case certainly gave Federal’s management no vested right to receive the benefits of such an order. See Federal Communications Commission v. Pottsville Broadcasting Co., 309 U. S. 134, 145. After the remand was made, therefore, the Commission was bound to deal with the problem afresh, performing the function delegated to it by Congress. It was again charged with the duty of measuring the proposed treatment of the management’s preferred stock holdings by relevant and proper standards. Only in that way could the legislative policies embodied in the Act be effectuated. Cf. Labor Board v. Donnelly Co., 330 U. S. 219, 227-228.
  The absence of a general rule or regulation governing management trading during reorganization did not affect the Commission’s duties in relation to the particular proposal before it. The Commission was asked to grant or deny effectiveness to a proposed amendment to Federal’s reorganization plan whereby the management would be accorded parity treatment on its holdings. It could do that only in the form of an order, entered after a due consideration of the particular facts in light of the relevant and proper standards. That was true regardless of whether those standards previously had been spelled out in a general rule or regulation. Indeed, if the Commission rightly felt that the proposed amendment was inconsistent with those standards, an order giving effect to the amendment merely because there was no general rule or regulation covering the matter would be unjustified.
  It is true that our prior decision explicitly recognized the possibility that the Commission might have promulgated a general rule dealing with this problem under its statutory rule-making powers, in which case the issue for our consideration would have been entirely different from that which did confront us. 318 U. S. 92-93. But we did not mean to imply thereby that the failure of the Commission to anticipate this problem and to promulgate a general rule withdrew all power from that agency to perform its statutory duty in this case. To hold that the Commission had no alternative in this proceeding but to approve the proposed transaction, while formulating any general rules it might desire for use in future cases of this nature, would be to stultify the administrative process. That we refuse to do.
  Since the Commission, unlike a court, does have the ability to make new law prospectively through the exercise of its rule-making powers, it has less reason to rely upon ad hoc adjudication to formulate new standards of conduct within the framework of the Holding Company Act. The function of filling in the interstices of the Act should be performed, as much as possible, through this quasi-legislative promulgation of rules to be applied in the future. But any rigid requirement to that effect would make the administrative process inflexible and incapable of dealing with many of the specialized problems which arise. See Report of the Attorney General’s Committee on Administrative Procedure in Government Agencies, S. Doc. No. 8, 77th Cong., 1st Sess., p. 29. Not every principle essential to the effective administration of a statute can or should be cast immediately into the mold of a general rule. Some principles must await their own development, while others must be adjusted to meet particular, unforeseeable situations. In performing its important functions in these respects, therefore, an administrative agency must be equipped to act either by general rule or by individual order. To insist upon one form of action to the exclusion of the other is to exalt form over necessity.
  In other words, problems may arise in a case which the administrative agency could not reasonably foresee, problems which must be solved despite the absence of a relevant general rule. Or the agency may not have had sufficient experience with a particular problem to warrant rigidifying its tentative judgment into a hard and fast rule. Or the problem may be so specialized and varying in nature as to be impossible of capture within the boundaries of a general rule. In those situations, the agency must retain power to deal with the problems on a case-to-case basis if the administrative process is to be effective. There is thus a very definite place for the case-by-case evolution of statutory standards. And the choice made between proceeding by general rule or by individual, ad hoc litigation is one that lies primarily in the informed discretion of the administrative agency. See Columbia Broadcasting System v. United States, 316 U. S. 407, 421.
  Hence we refuse to say that the Commission, which had not previously been confronted with the problem of management trading during reorganization, was forbidden from utilizing this particular proceeding for announcing and applying a new standard of conduct. Cf. Federal Trade Commission v. Keppel & Bro., 291 U. S. 304. That such action might have a retroactive effect was not necessarily fatal to its validity. Every case of first impression has a retroactive effect, whether the new principle is announced by a court or by an administrative agency. But such retroactivity must be balanced against the mischief of producing a result which is contrary to a statutory design or to legal and equitable" principles. If that mischief is greater than the ill effect of the retroactive application of a new standard, it is not the type of retroactivity which is condemned by law. See Addison v. Holly Hill Co., 322 U. S. 607, 620.
  And so in this case, the fact that the Commission’s order might retroactively prevent Federal’s management from securing the profits and control which were the objects of the preferred stock purchases may well be outweighed by the dangers inherent in such purchases from the statutory standpoint. If that is true, the argument of retroactivity becomes nothing more than a claim that the Commission lacks power to enforce the standards of the Act in this proceeding. Such a claim deserves rejection.
  The problem in this case thus resolves itself into a determination of whether the Commission’s action in denying effectiveness to the proposed amendment to the Federal reorganization plan can be justified on the basis upon which it clearly rests. As we have noted, the Commission avoided placing its sole reliance on inapplicable judicial precedents. Rather it has derived its conclusions from the particular facts in the case, its general experience in reorganization matters and its informed view of statutory requirements. It is those matters which are the guide for our review.
  The Commission concluded that it could not find that the reorganization plan, if amended as proposed, would be “fair and equitable to the persons affected thereby” within the meaning of § 11 (e) of the Act, under which the reorganization was taking place. Its view was that the amended plan would involve the issuance of securities on terms “detrimental to the public interest or the interest of investors” contrary to §§ 7 (d) (6) and 7 (e), and would result in an “unfair or inequitable distribution of voting power” among the Federal security holders within the meaning of § 7 (e). It was led to this result “not by proof that the interveners [Federal’s management] committed acts of conscious wrongdoing but by the character of the conflicting interests created by the interveners’ program of stock purchases carried out while plans for reorganization were under consideration.”
  The Commission noted that Federal’s management controlled a large multi-state utility system and that its influence permeated down to the lowest tier of operating companies. The financial, operational and accounting policies of the parent and its subsidiaries were therefore under the management’s strict control. The broad range of business judgments vested in Federal’s management multiplied opportunities for affecting the market price of Federal’s outstanding securities and made the exercise of judgment on any matter a subject of greatest significance to investors. Added to these normal managerial powers, the Commission pointed out that a holding company management obtains special powers in the course of a voluntary reorganization under § 11 (e) of the Holding Company Act. The management represents the stockholders in such a reorganization, initiates the proceeding, draws up and files the plan, and can file amendments thereto at any time. These additional powers may introduce conflicts between the management’s normal interests and its responsibilities to the various classes of stockholders which it represents in the reorganization. Moreover, because of its representative status, the management has special opportunities to obtain advance information of the attitude of the Commission.
  Drawing upon its experience,-the Commission indicated that all these normal and special powers of the holding company management during the course of a § 11 (e) reorganization placed in the management’s command “a formidable battery of devices that would enable it, if it should choose to use them selfishly, to affect in material degree the ultimate allocation of new securities among the various existing classes, to influence the market for its own gain, and to manipulate or obstruct the reorganization required by the mandate of the statute.” In that setting, the Commission felt that a management program of stock purchase would give rise to the temptation and the opportunity to shape the reorganization proceeding so as to encourage public selling on the market at low prices. No management could engage in such a program without raising serious questions as to whether its personal interests had not opposed its duties “to exercise disinterested judgment in matters pertaining to subsidiaries’ accounting, budgetary and dividend policies, to present publicly an unprejudiced financial picture of the enterprise, and to effectuate a fair and feasible plan expeditiously.”
  The Commission further felt that its answer should be the same even where proof of intentional wrongdoing on the management’s part is lacking. Assuming a conflict of interests, the Commission thought that the absence of actual misconduct is immaterial; injury to the public investors and to the corporation may result just as readily. “Questionable transactions may be explained away, and an abuse of investors and the administrative process may be perpetrated without evil intent, yet the injury will remain.” Moreover, the Commission was of the view that the delays and the difficulties involved in probing the mental processes and personal integrity of corporate officials do not warrant any distinction on the basis of evil intent, the plain fact being “that an absence of unfairness or detriment in cases of this sort would be practically impossible to establish by proof.”
  Turning to the facts in this case, the Commission noted the salient fact that the primary object of Federal’s management in buying the preferred stock was admittedly to obtain the voting power that was accruing to that stock through the reorganization and to profit from the investment therein. That stock had been purchased in the market at prices that were depressed in relation to what the management anticipated would be, and what in fact was, the earning and asset value of its reorganization equivalent. The Commission admitted that the good faith and personal integrity of this management were not in question; but as to the management’s justification of its motives, the Commission concluded that it was merely trying to “deny that they made selfish use of their powers during the period when their conflict of interest, vis-a-vis public investors, was in existence owing to their purchase program.” Federal’s management had thus placed itself in a position where it was “peculiarly susceptible to temptation to conduct the reorganization for personal gain rather than the public good” and where its desire to make advantageous purchases of stock could have an important influence, even though subconsciously, upon many of the decisions to be made in the course of the reorganization. Accordingly, the Commission felt that all of its general considerations of the problem were applicable to this case.
  The scope of our review of an administrative order wherein a new principle is announced and applied is no different from that which pertains to ordinary administrative action. The wisdom of the principle adopted is none of our concern. See Board of Trade v. United States, 314 U. S. 534, 548. Our duty is at an end when it becomes evident that the Commission’s action is based upon substantial evidence and is consistent with the authority granted by Congress. See National Broadcasting Co. v. United States, 319 U. S. 190, 224.
  We are unable to say in this case that the Commission erred in reaching the result it did. The facts being undisputed, we are free to disturb the Commission’s conclusion only if it lacks any rational and statutory foundation. In that connection, the Commission has made a thorough examination of the problem, utilizing statutory standards and its own accumulated experience with reorganization matters. In essence, it has made what we indicated in our prior opinion would be an informed, expert judgment on the problem. It has taken into account “those more subtle factors in the marketing of utility company securities that gave rise to the very grave evils which the Public Utility Holding [Company] Act of 1935 was designed to correct” and has relied upon the fact that “Abuse of corporate position, influence, and access to information may raise questions so subtle that the law can deal with them effectively only by pfóhibitions not concerned with the fairness of a particular transaction.” 318 U. S. at 92.
  Such factors may properly be considered by the Commission in determining whether to approve a plan of reorganization of a utility holding company, or an amendment to such a plan. The “fair and equitable” rule of § 11 (e) and the standard of what is “detrimental to the public interest or the interest of investors or consumers” under § 7 (d) (6) and § 7 (e) were inserted by the framers of the Act in order that the Commission might have broad powers to protect the various interests at stake. 318 U. S. at 90-91. The application of those criteria, whether in the form of a particular order or a general regulation, necessarily requires the use of informed discretion by the Commission. The very breadth of the statutory language precludes a reversal of the Commission’s judgment save where it has plainly abused its discretion in these matters. See United States v. Lowden, 308 U. S. 225; I. C. C. v. Railway Labor Assn., 315 U. S. 373. Such an abuse is not present in this case.
  The purchase by a holding company management of that company’s securities during the course of a reorganization may well be thought to be so fraught with danger as to warrant a denial of the benefits and profits accruing to the management. The possibility that such a stock purchase program will result in detriment to the public investors is not a fanciful one. The influence that program may have upon the important decisions to be made by the management during reorganization is not inconsequential. Since the officers and directors occupy fiduciary positions during this period, their actions are to be held to a higher standard than that imposed upon the general investing public. There is thus a reasonable basis for a judgment that the benefits and profits accruing to the management from the stock purchases should be prohibited, regardless of the good faith involved. And it is a judgment that can justifiably be reached in terms of fairness and equitableness, to the end that the interests of the public, the investors and the consumers might be protected. But it is a judgment based upon public policy, a judgment which Congress has indicated is of the type for the Commission to make.
  The Commission’s conclusion here rests squarely in that area where administrative judgments are entitled to the greatest amount of weight by appellate courts. It is the product of administrative experience, appreciation of the complexities of the problem, realization of the statutory policies, and responsible treatment of the uncontested facts. It is the type of judgment which administrative agencies are best equipped to make and which justifies the use of the administrative process. See Republic Aviation Corp. v. Labor Board, 324 U. S. 793, 800. Whether we agree or disagree with the result reached, it is an allowable judgment which we cannot disturb.
  Reversed.
  Mr. Justice Burton concurs in the result.
  The Chief Justice and Mr. Justice Douglas took no part in the consideration or decision of these cases.
  Mr. Justice Frankfurter and Mr. Justice Jackson dissent, but there is not now opportunity for a response adequate to the issues raised by the Court’s opinion. These concern the rule of law in its application to the administrative process and the function of this Court in reviewing administrative action. Accordingly, the detailed grounds for dissent will be filed in due course.