delivered the opinion of the Court:
1. If there is one question that ought to be regarded as settled, it is that the courts of the United States will not undertake, through the process of mandamus, to control the exercise of discretion by an executive officer of the Government in the performance of the duties entrusted to him.
“To the judiciary department is entrusted generally the interpretation of the laws, the determination of rights and the application of remedies, and'with the strong sense of their duties and obligations in this regard it is sometimes difficult for the courts to properly appreciate the fact, that the executive department is charged with perfectly independent duties, not alone by the supreme law, but also by legislation thereunder, which require the ascertainment of facts, involve the interpretation of laws, and in many respects call for the exercise of judgment and discretion by *505officers who are not required to be lawyers. And this independence is so complete, that no matter how gross an error may be committed, or however ill advised the action of an executive officer may be, in the execution of these duties, the courts are nevertheless powerless to interfere where no appeal to them is given. Public and private interests may suffer in instances, and rights may sometimes be denied; but these alone do not authorize the interference of the courts with the duties of executive officers. Greater evils could not exist under our system of government than would follow the usurpation by the.judiciary of powers not entrusted to them.” Seymour v. South Carolina, 2 App. D. C. 240, 245.
In a case involving the construction of one of the pension acts, which is under consideration here, the Supreme Court of the United States said: “ The court will not interfere by mandamus with the executive officers of the Government in the exercise of their ordinary official duties, even where those duties require an interpretation of the law, the court having no appellate power for that purpose.” United States, ex. rel. Dunlap v. Black, 128 U. S. 40, 48.
The act of the Commissioner of Pensions in this case, if he had the power to act at all (a point that will be considered later), necessarily involved the exeixise of judgment and discretion; it depended upon an interpretation of the pension laws and the application thereof to the facts of re lator’s case.
It cannot be said that this was a matter of ready determination and free of all doubt. The two justices of the Supreme Court of the District, before whom the question has been raised, have differed with each other in opinions expressed thereon.. One, Mr. Justice Cox, agrees with the Commissioner, while the other, Mr. Justice Bradley, has taken the opposite view. We have not considered the question as one for our determination and shall express no opinion on it. Nor are we to be understood, from the conclusion arrived at in this case, as intimating any opinion *506with respect to relator’s claim to the rating from which he has been reduced by the action complained of in his petition. As was said in the case of Dunlap v. Black, supra:“ Whether if the law were properly before us for consideration we should be of the same opinion, or of a different opinion, is of no consequence in the decision of this case. We have no appellate power over the Commissioner, and no right to review his decision. That decision and his action taken thereon were made and done in the exercise of his official functions. They were by no means merely ministerial acts.”
Whether the power shall be exercised by the courts of this District, or by a special tribunal created for the purpose, to review the action of the Commissioner of Pensions in awarding or denying, in increasing or decreasing pensions, is a matter within the exclusive jurisdiction of Congress. Though necessarily aware of the long-established rule of non-interference by the courts in such matters, Congress has not seen fit to adopt a new rule in the premises, or to give a remedy in the courts to an aggrieved party. On the contrary, a qualified jurisdiction which seems to have once existed in the Court of Claims, over pension claims, was expressly taken away by a provision in the act of March 3, 1877, ch. 359, sec. 1.
2. Before proceeding further, we deem it proper to advert to a question of procedure, apparent on the record, lest we might be understood as giving our unqualified sanction to the course that has been pursued. Relator did not seek to exercise his undoubted right of appeal to the Secretary of the Interior from the ruling of the Commissioner. This he should have done. Even where the right to the writ is otherwise clear, still, it will not issue where there is another plain, legal remedy. The reasons for not having exercised this right of appeal are insufficient. But the Secretary, in his answer, expressly waives this condition and defends on other grounds. If the exercise of the right of appeal to him was necessary to the jurisdiction of the *507court, it is clear that his waiver could not cure the defect. If not jurisdictional, in that sense, but rather a question of privilege on his part, then he could waive it.
The decision of this question is not necessary in our view of the whole case, and as it has not been argued we will pass it by, remarking only that it is one of doubt, and that we are not to be understood as acquiescing in the Secretary’s right to waive the point and compel action by the court, in consequence.
3. It is earnestly contended, on behalf of the relator, that his pension rate having been adjudicated by Commissioner Tanner, became a fixed and vested legal right beyond the power of a succeeding Commissioner to disturb except tor actual misrepresentation and fraud. If this contention be well founded the judgment must stand. United States v. Schurz, 102 U. S. 378; Noble v. Union River Logging Co., 147 U. S. 165.
On the other hand, the respondent contends that it is both the right and the duty of the Commissioner of Pensions to correct the rating of the pensioner whenever informed and satisfied of its illegality, without regard to its original procurement by actual fraud. He further claims an estoppel, on the part of relator, to deny this authority, because the rating which he seeks to maintain depends upon a ruling of Commissioner Tanner, setting aside, for error of law, the previous ruling in his case made by Commissioner Dudley. To this it is replied that a new ruling may be made at any time in favor of a pensioner, but never against him, and for that purpose his case may always be considered as open. We find no reasonable support for this one-sided view. Surely, if the right exists to set aside. a former decision, made upon the same facts, because it was founded in mistake of law and thereby deprived the applicant of a just claim under a correct interpretation of the statute, the same right ought to exist, in favor of the Government, to reduce a payment, the full amount of which is without legal foundation. In this view, then, if a decision *508of the Commissioner were to be regarded as res judicata, that made by Commissioner Tanner, raising relator’s rate, was without authority and void, and the present Commissioner would be justified, for that reason alone, in returning him to the rate fixed by the decision of Commissioner Dudley.
To what extent the decision of one Secretary, or head of department, shall be considered as binding upon his successors, has never been regulated by statute nor fully settled by judicial decision.
In matters relating to grants of land it is settled that where the decision has been made and all the requisites of the law complied with, the title becomes vested, in so far as the executive power is concerned, and cannot be recalled. It can only be avoided thereafter by proceeding in a court for fraud or illegality. United States v. Schurz, 102 U. S. 378, 402; Noble v. Union River Logging Co., 147 U. S. 165, 175.
So, where the right of a third person has attached under a decision made, a settlement had, or an account stated, it cannot be' divested, or impaired, by the subsequent action of a successor in office. United States v. Bank of Metropolis, 15 Pet. 377. Notwithstanding some remarks made in the opinion in that case, considered apart from its facts, would sustain the view that the action of Postmaster General Barry, in making certain allowances to a contractor, could not be reviewed by his successor, it is nevertheless reasonably plain that they had relation to the fact that the allowances had been made and the right of the bank had accrued, through indorsement to it in due course of business, of a draft accepted by the Postmaster General upon the foundation of that settlement. Concluding its remarks-, the court said : “ It is no longer a case between the correctness of one officer’s judgment and that of his successor. A third party is interested and he cannot be deprived of a payment on a credit so given, but by the intervention of a court to pass upon his right.”
*509In another case, where a sum of money had been paid to a naval officer by the Secretary of the Navy to cover certain expenses allowed by him, the power of the accounting officers of the Treasury, to overrule the Secretary, declare his payment without authority, and deduct the sum so paid from the pay due the officer, was denied. United States v. Jones, 18 How. 92, 95. That case is readily distinguishable from this. In United States v. Johnston, 124 U. S. 236, 253, 255, which was a suit to recover certain moneys paid upon the allowance by the Secretary of the Treasury of an agent’s expense account, after the lapse of many years from the date of settlement, the court held that the account could not be attacked for irregularity or mistakes because of insufficient evidence, especially after such great lapse of time. It was said, however, that the approval of the account by the Secretary “ would not be conclusive, if it appeared either that such approval was procured by fraud, or that such expenses were incurred in violation of some positive statute, or in contravention of public policy.”
Subject to the foregoing limitations, it can be said that no case has denied the doctrine enounced in United States v. MacDaniel, 7 Pet. 1, as follows: “It will not be contended that one Secretary has not the same power as another to give a construction to an act which relates to the business of his office.”
In this case the ruling does not affect, or attempt to affect the right of relator to retain the large sums of money which he has received under the decision of Commissioner Tanner. That might present a very different question. The right of no third person has intervened; nor could it, because the pension is not transferable and not subject to claims of creditors.
The pension certificate itself is the creature of department practice and has no function analogous to a patent or a grant. The claim to the pension is not a vested, legal right. It is a bounty that may be given or recalled, increased or diminished at the pleasure of Congress. Walton *510v. Cotton, 19 How. 355; United States v. Teller, 107 U. S. 64, 68; Frisbie v. United States, 157 U. S. 160, 166.
The practice of reconsideration for error or illegality seems to have prevailed in the Pension Office from a very early period. A proceeding in the case of Captain Somerville, as early as 1803, and certain decisions made under later pension laws, cited in the brief of respondent, sustain this view. Dig. pp. 398, 399, 435. Scofield, J., in Harrison v. United States, 20 Ct. Claims Rep. 122, 126, states the rule and the reasons for its existence very strongly as follows : “ The power of revision may well be considered to be inherent in the nature of the first decision as well as in the necessities of the bureau. The pension is a gratuity. It involves no claim of right, no agreements of parties and, as it is not assignable, no acquired rights of third parties. The law describes a class of persons upon whom it chooses to bestow its bounty. The Secretary and Commissioner are directed to find out and make a list of persons thus described. The proceedings and evidence are largely ex parte. From the vast number of applicants, the work must be performed and the roll made up, for the most .part by the clerks. If placing the name of an applicant upon the roll is to be considered a judicial act, should it not be considered only a judgment nisi?"
The court will take notice of a long continued usage or practice in the executive departments. United States v. Bailey, 9 Pet. 238, 255. And such practice and the interpretation given to statutes, and the powers exercised thereunder are entitled to very great weight. The Laura, 114 U. S. 411, 416; United States v. Hill, 120 U. S. 169, 182.
Certain provisions of the pension acts, antedating the first action in relator’s case, seem to recognize the existence of the practice, and this recognition is especially plain in the act of June 21, 1879, which repeals certain sections of the Revised Statutes and concludes with this proviso : “ Provided, that the Commissioner of Pensions shall have the same power as heretofore to order special examinations, *511whenever in his judgment the same may be necessary, and to increase or reduce the pension according to right and justice
There are, as we have seen, very strong reasons for holding that where a title has passed, or the rights of innocent third persons have supervened, or there has been a very great lapse of time, without question, the decisions of the head of an executive department should be considered as beyond the power of his successors to disturb.
The reasons are quite” strong also, why, as to transactions wholly ended, where credit has been given or money paid over, there should be no recognized right of review save for fraud or manifest illegality. But where the matter is one that involves future recurring payments of money there seems no good reason why succeeding incumbents of the office, charged with a present responsibility, should be concluded by the decisions of their predecessors. 'They should not lightly overrule their predecessors ; but when satisfied and convinced that error has been committed and that there is no legal warrant for the payment demanded, it would seem to be their duty, as well as their right, to rectify the error. The recognition of the power in such cases involves no destruction of vested rights, no impairment of the obligations of contracts, and no abridgment of the equities of third persons. It is a question simply of the proper performance of a present duty, the conscientious discharge of a present obligation. This seems to be the rule that has prevailed in the Treasury Department in analogous cases. It is entirely within the regulating power of Congress, if found unsatisfactory. We have heretofore referred to certain provisions of the statutes as recognizing the existence of the power exercised by the respondent in this case. But since this controversy arose, though prior to the particular act complained of in this case, a statute has been enacted which distinctly legalizes the practice pursued by respondent. Presumably to meet complaints prevalent concerning the action of the Pension Office in' *512suspending and reducing pensions the following provision was inserted in the appropriation act of December 21, 1893 : “ Provided that any pension heretofor'e or that may hereafter be granted to any applicant therefor under any law of the United States authorizing the granting and payment of pensions, on application made and adjudicated upon, shall be deemed and held by all officers of the United States to be a vested right in the grantee to that extent that payment thereof shall not be withheld or suspended until, after due notice to the grantee of not less than thirty days, the Commissioner of Pensions, after hearing all the evidence, shall decide to annul, vacate, modify, or set aside the decision upon which such pension was granted. Such notice to grantee must contain a full and true statement of any charges or allegations upon which such decision granting such pension shall be sought to be in any manner disturbed or modified.”
In this statute, for the first time, the pension is recognized as a vested right and then to an extent only that prevents its summary suspension or abrogation; at the same time the right “ to annul, vacate, modify, or set aside the decision ” upon which a pension has been granted is distinctly and fully recognized.
Holding, as we must do, that the respondent, as Commissioner of Pensions, had the power to review and modify the decision of the former Commissioner in relator’s case and reduce his rating, and that the exercise of this power was a matter of judgment and discretion in the discharge of his official duties, over which the courts have no control, it follows that the judgment appealed from must be reversed, -with costs to the appellee, and relateds petition dismissed. And it is so ordered.