JUSTICE O'CONNOR delivered the opinion of the Court.
This case requires us to consider the proper standards for judging a criminal defendant's contention that the Constitution requires a conviction or death sentence to be set aside because counsel's assistance at the trial or sentencing was ineffective.
I
A
During a 10-day period in September, 1976, respondent planned and committed three groups of crimes, which included three brutal stabbing murders, torture, kidnaping, severe assaults, attempted murders, attempted extortion, and theft. After his two accomplices were arrested, respondent surrendered to police and voluntarily gave a lengthy statement confessing to the third of the criminal episodes. The State of Florida indicted respondent for kidnaping and murder and appointed an experienced criminal lawyer to represent him.
Counsel actively pursued pretrial motions and discovery. He cut his efforts short, however, and he experienced a sense of hopelessness about the case, when he learned that, against his specific advice, respondent had also confessed to the first two murders. By the date set for trial, respondent was subject to indictment for three counts of first-degree murder and multiple counts of robbery, kidnaping for ransom, breaking and entering and assault, attempted murder, and conspiracy to commit robbery. Respondent waived his right to a jury trial, again acting against counsel's advice, and pleaded guilty to all charges, including the three capital murder charges.
In the plea colloquy, respondent told the trial judge that, although he had committed a string of burglaries, he had no significant prior criminal record, and that, at the time of his criminal spree, he was under extreme stress caused by his inability to support his family. App. 50-53. He also stated, however, that he accepted responsibility for the crimes. E.g., id. at 54, 57. The trial judge told respondent that he had "a great deal of respect for people who are willing to step forward and admit their responsibility," but that he was making no statement at all about his likely sentencing decision. Id. at 62.
Counsel advised respondent to invoke his right under Florida law to an advisory jury at his capital sentencing hearing. Respondent rejected the advice and waived the right. He chose instead to be sentenced by the trial judge without a jury recommendation.
In preparing for the sentencing hearing, counsel spoke with respondent about his background. He also spoke on the telephone with respondent's wife and mother, though he did not follow up on the one unsuccessful effort to meet with them. He did not otherwise seek out character witnesses for respondent. App. to Pet. for Cert. A265. Nor did he request a psychiatric examination, since his conversations with his client gave no indication that respondent had psychological problems. Id. at A266.
Counsel decided not to present, and hence not to look further for, evidence concerning respondent's character and emotional state. That decision reflected trial counsel's sense of hopelessness about overcoming the evidentiary effect of respondent's confessions to the gruesome crimes. See id. at A282. It also reflected the judgment that it was advisable to rely on the plea colloquy for evidence about respondent's background and about his claim of emotional stress: the plea colloquy communicated sufficient information about these subjects, and by forgoing the opportunity to present new evidence on these subjects, counsel prevented the State from cross-examining respondent on his claim and from putting on psychiatric evidence of its own. Id. at A223-A225.
Counsel also excluded from the sentencing hearing other evidence he thought was potentially damaging. He successfully moved to exclude respondent's "rap sheet." Id. at A227; App. 311. Because he judged that a presentence report might prove more detrimental than helpful, as it would have included respondent's criminal history and thereby would have undermined the claim of no significant history of criminal activity, he did not request that one be prepared. App. to Pet. for Cert. A227-A228, A265-A266.
At the sentencing hearing, counsel's strategy was based primarily on the trial judge's remarks at the plea colloquy as well as on his reputation as a sentencing judge who thought it important for a convicted defendant to own up to his crime. Counsel argued that respondent's remorse and acceptance of responsibility justified sparing him from the death penalty. Id. at A265-A266. Counsel also argued that respondent had no history of criminal activity, and that respondent committed the crimes under extreme mental or emotional disturbance, thus coming within the statutory list of mitigating circumstances. He further argued that respondent should be spared death because he had surrendered, confessed, and offered to testify against a codefendant, and because respondent was fundamentally a good person who had briefly gone badly wrong in extremely stressful circumstances. The State put on evidence and witnesses largely for the purpose of describing the details of the crimes. Counsel did not cross-examine the medical experts who testified about the manner of death of respondent's victims.
The trial judge found several aggravating circumstances with respect to each of the three murders. He found that all three murders were especially heinous, atrocious, and cruel, all involving repeated stabbings. All three murders were committed in the course of at least one other dangerous and violent felony, and since all involved robbery, the murders were for pecuniary gain. All three murders were committed to avoid arrest for the accompanying crimes and to hinder law enforcement. In the course of one of the murders, respondent knowingly subjected numerous persons to a grave risk of death by deliberately stabbing and shooting the murder victim's sisters-in-law, who sustained severe -in one case, ultimately fatal -injuries.
With respect to mitigating circumstances, the trial judge made the same findings for all three capital murders. First, although there was no admitted evidence of prior convictions, respondent had stated that he had engaged in a course of stealing. In any case, even if respondent had no significant history of criminal activity, the aggravating circumstances "would still clearly far outweigh" that mitigating factor. Second, the judge found that, during all three crimes, respondent was not suffering from extreme mental or emotional disturbance, and could appreciate the criminality of his acts. Third, none of the victims was a participant in, or consented to, respondent's conduct. Fourth, respondent's participation in the crimes was neither minor nor the result of duress or domination by an accomplice. Finally, respondent's age (26) could not be considered a factor in mitigation, especially when viewed in light of respondent's planning of the crimes and disposition of the proceeds of the various accompanying thefts.
In short, the trial judge found numerous aggravating circumstances and no (or a single comparatively insignificant) mitigating circumstance. With respect to each of the three convictions for capital murder, the trial judge concluded:
A careful consideration of all matters presented to the court impels the conclusion that there are insufficient mitigating circumstances… to outweigh the aggravating circumstances.
See Washington v. State, 362 So.2d 658, 663-664 (Fla.1978) (quoting trial court findings), cert. denied, 441 U.S. 937 (1979). He therefore sentenced respondent to death on each of the three counts of murder and to prison terms for the other crimes. The Florida Supreme Court upheld the convictions and sentences on direct appeal.
B
Respondent subsequently sought collateral relief in state court on numerous grounds, among them that counsel had rendered ineffective assistance at the sentencing proceeding. Respondent challenged counsel's assistance in six respects. He asserted that counsel was ineffective because he failed to move for a continuance to prepare for sentencing, to request a psychiatric report, to investigate and present character witnesses, to seek a presentence investigation report, to present meaningful arguments to the sentencing judge, and to investigate the medical examiner's reports or cross-examine the medical experts. In support of the claim, respondent submitted 14 affidavits from friends, neighbors, and relatives stating that they would have testified if asked to do so. He also submitted one psychiatric report and one psychological report stating that respondent, though not under the influence of extreme mental or emotional disturbance, was "chronically frustrated and depressed because of his economic dilemma" at the time of his crimes. App. 7; see also id. at 14.
The trial court denied relief without an evidentiary hearing, finding that the record evidence conclusively showed that the ineffectiveness claim was meritless. App. to Pet. for Cert. A206-A243. Four of the assertedly prejudicial errors required little discussion. First, there were no grounds to request a continuance, so there was no error in not requesting one when respondent pleaded guilty. Id. at A218-A220. Second, failure to request a presentence investigation was not a serious error because the trial judge had discretion not to grant such a request and because any presentence investigation would have resulted in admission of respondent's "rap sheet," and thus would have undermined his assertion of no significant history of criminal activity. Id. at A226-A228. Third, the argument and memorandum given to the sentencing judge were "admirable" in light of the overwhelming aggravating circumstances and absence of mitigating circumstances. Id. at A228. Fourth, there was no error in failure to examine the medical examiner's reports or to cross-examine the medical witnesses testifying on the manner of death of respondent's victims, since respondent admitted that the victims died in the ways shown by the unchallenged medical evidence. Id. at A229.
The trial court dealt at greater length with the two other bases for the ineffectiveness claim. The court pointed out that a psychiatric examination of respondent was conducted by state order soon after respondent's initial arraignment. That report states that there was no indication of major mental illness at the time of the crimes. Moreover, both the reports submitted in the collateral proceeding state that, although respondent was "chronically frustrated and depressed because of his economic dilemma," he was not under the influence of extreme mental or emotional disturbance. All three reports thus directly undermine the contention made at the sentencing hearing that respondent was suffering from extreme mental or emotional disturbance during his crime spree. Accordingly, counsel could reasonably decide not to seek psychiatric reports; indeed, by relying solely on the plea colloquy to support the emotional disturbance contention, counsel denied the State an opportunity to rebut his claim with psychiatric testimony. In any event, the aggravating circumstances were so overwhelming that no substantial prejudice resulted from the absence at sentencing of the psychiatric evidence offered in the collateral attack.
The court rejected the challenge to counsel's failure to develop and to present character evidence for much the same reasons. The affidavits submitted in the collateral proceeding showed nothing more than that certain persons would have testified that respondent was basically a good person who was worried about his family's financial problems. Respondent himself had already testified along those lines at the plea colloquy. Moreover, respondent's admission of a course of stealing rebutted many of the factual allegations in the affidavits. For those reasons, and because the sentencing judge had stated that the death sentence would be appropriate even if respondent had no significant prior criminal history, no substantial prejudice resulted from the absence at sentencing of the character evidence offered in the collateral attack.
Applying the standard for ineffectiveness claims articulated by the Florida Supreme Court in Knight v. State, 394 So.2d 997 (1981), the trial court concluded that respondent had not shown that counsel's assistance reflected any substantial and serious deficiency measurably below that of competent counsel that was likely to have affected the outcome of the sentencing proceeding. The court specifically found:
[A]s a matter of law, the record affirmatively demonstrates beyond any doubt that even if [counsel] had done each of the… things [that respondent alleged counsel had failed to do] at the time of sentencing, there is not even the remotest chance that the outcome would have been any different. The plain fact is that the aggravating circumstances proved in this case were completely overwhelming….
App. to Pet. for Cert. A230.
The Florida Supreme Court affirmed the denial of relief. Washington v. State, 397 So.2d 285 (1981). For essentially the reasons given by the trial court, the State Supreme Court concluded that respondent had failed to make out a prima facie case of either "substantial deficiency or possible prejudice" and, indeed, had "failed to such a degree that we believe, to the point of a moral certainty, that he is entitled to no relief…." Id. at 287. Respondent's claims were "shown conclusively to be without merit, so as to obviate the need for an evidentiary hearing." Id. at 286.
C
Respondent next filed a petition for a writ of habeas corpus in the United States District Court for the Southern District of Florida. He advanced numerous grounds for relief, among them ineffective assistance of counsel based on the same errors, except for the failure to move for a continuance, as those he had identified in state court. The District Court held an evidentiary hearing to inquire into trial counsel's efforts to investigate and to present mitigating circumstances. Respondent offered the affidavits and reports he had submitted in the state collateral proceedings; he also called his trial counsel to testify. The State of Florida, over respondent's objection, called the trial judge to testify.
The District Court disputed none of the state court factual findings concerning trial counsel's assistance and made findings of its own that are consistent with the state court findings. The account of trial counsel's actions and decisions given above reflects the combined findings. On the legal issue of ineffectiveness, the District Court concluded that, although trial counsel made errors in judgment in failing to investigate nonstatutory mitigating evidence further than he did, no prejudice to respondent's sentence resulted from any such error in judgment. Relying in part on the trial judge's testimony but also on the same factors that led the state courts to find no prejudice, the District Court concluded that "there does not appear to be a likelihood, or even a significant possibility" that any errors of trial counsel had affected the outcome of the sentencing proceeding. App. to Pet. for Cert. A285-A286. The District Court went on to reject all of respondent's other grounds for relief, including one not exhausted in state court, which the District Court considered because, among other reasons, the State urged its consideration. Id. at A286-A292. The court accordingly denied the petition for a writ of habeas corpus.
On appeal, a panel of the United States Court of Appeals for the Fifth Circuit affirmed in part, vacated in part, and remanded with instructions to apply to the particular facts the framework for analyzing ineffectiveness claims that it developed in its opinion. 673 F.2d 879 (1982). The panel decision was itself vacated when Unit B of the former Fifth Circuit, now the Eleventh Circuit, decided to rehear the case en banc. 679 F.2d 23 (1982). The full Court of Appeals developed its own framework for analyzing ineffective assistance claims and reversed the judgment of the District Court and remanded the case for new factfinding under the newly announced standards. 693 F.2d 1243 (1982).
The court noted at the outset that, because respondent had raised an unexhausted claim at his evidentiary hearing in the District Court, the habeas petition might be characterized as a mixed petition subject to the rule of Rose v. Lundy, 455 U. S. 509 (1982), requiring dismissal of the entire petition. The court held, however, that the exhaustion requirement is "a matter of comity, rather than a matter of jurisdiction," and hence admitted of exceptions. The court agreed with the District Court that this case came within an exception to the mixed petition rule. 693 F.2d at 1248, n. 7.
Turning to the merits, the Court of Appeals stated that the Sixth Amendment right to assistance of counsel accorded criminal defendants a right to "counsel reasonably likely to render and rendering reasonably effective assistance given the totality of the circumstances." Id. at 1250. The court remarked in passing that no special standard applies in capital cases such as the one before it: the punishment that a defendant faces is merely one of the circumstances to be considered in determining whether counsel was reasonably effective. Id. at 1250, n. 12. The court then addressed respondent's contention that his trial counsel's assistance was not reasonably effective because counsel breached his duty to investigate nonstatutory mitigating circumstances.
The court agreed that the Sixth Amendment imposes on counsel a duty to investigate, because reasonably effective assistance must be based on professional decisions and informed legal choices can be made only after investigation of options. The court observed that counsel's investigatory decisions must be assessed in light of the information known at the time of the decisions, not in hindsight, and that "[t]he amount of pretrial investigation that is reasonable defies precise measurement." Id. at 1251. Nevertheless, putting guilty plea cases to one side, the court attempted to classify cases presenting issues concerning the scope of the duty to investigate before proceeding to trial.
If there is only one plausible line of defense, the court concluded, counsel must conduct a "reasonably substantial investigation" into that line of defense, since there can be no strategic choice that renders such an investigation unnecessary. Id. at 1252. The same duty exists if counsel relies at trial on only one line of defense, although others are available. In either case, the investigation need not be exhaustive. It must include " an independent examination of the facts, circumstances, pleadings and laws involved.'" Id. at 1253 (quoting Rummel v. Estelle, 590 F.2d 103, 104 (CA 1979)). The scope of the duty, however, depends on such facts as the strength of the government's case and the likelihood that pursuing certain leads may prove more harmful than helpful. 693 F.2d at 1253, n. 16.
If there is more than one plausible line of defense, the court held, counsel should ideally investigate each line substantially before making a strategic choice about which lines to rely on at trial. If counsel conducts such substantial investigations, the strategic choices made as a result "will seldom if ever" be found wanting. Because advocacy is an art and not a science, and because the adversary system requires deference to counsel's informed decisions, strategic choices must be respected in these circumstances if they are based on professional judgment. Id. at 1254.
If counsel does not conduct a substantial investigation into each of several plausible lines of defense, assistance may nonetheless be effective. Counsel may not exclude certain lines of defense for other than strategic reasons. Id. at 1257-1258. Limitations of time and money, however, may force early strategic choices, often based solely on conversations with the defendant and a review of the prosecution's evidence. Those strategic choices about which lines of defense to pursue are owed deference commensurate with the reasonableness of the professional judgments on which they are based. Thus,
when counsel's assumptions are reasonable, given the totality of the circumstances, and when counsel's strategy represents a reasonable choice based upon those assumptions, counsel need not investigate lines of defense that he has chosen not to employ at trial.
Id. at 1255 (footnote omitted). Among the factors relevant to deciding whether particular strategic choices are reasonable are the experience of the attorney, the inconsistency of unpursued and pursued lines of defense, and the potential for prejudice from taking an unpursued line of defense. Id. at 1256-1257, n. 23.
Having outlined the standards for judging whether defense counsel fulfilled the duty to investigate, the Court of Appeals turned its attention to the question of the prejudice to the defense that must be shown before counsel's errors justify reversal of the judgment. The court observed that only in cases of outright denial of counsel, of affirmative government interference in the representation process, or of inherently prejudicial conflicts of interest had this Court said that no special showing of prejudice need be made. Id. at 1258-1259. For cases of deficient performance by counsel, where the government is not directly responsible for the deficiencies and where evidence of deficiency may be more accessible to the defendant than to the prosecution, the defendant must show that counsel's errors "resulted in actual and substantial disadvantage to the course of his defense." Id. at 1262. This standard, the Court of Appeals reasoned, is compatible with the "cause and prejudice" standard for overcoming procedural defaults in federal collateral proceedings, and discourages insubstantial claims by requiring more than a showing, which could virtually always be made, of some conceivable adverse effect on the defense from counsel's errors. The specified showing of prejudice would result in reversal of the judgment, the court concluded, unless the prosecution showed that the constitutionally deficient performance was, in light of all the evidence, harmless beyond a reasonable doubt. Id. at 1260-1262.
The Court of Appeals thus laid down the tests to be applied in the Eleventh Circuit in challenges to convictions on the ground of ineffectiveness of counsel. Although some of the judges of the court proposed different approaches to judging ineffectiveness claims either generally or when raised in federal habeas petitions from state prisoners, id. at 1264-1280 (opinion of Tjoflat, J.); id. at 1280 (opinion of Clark, J.); id. at 1285-1288 (opinion of Roney, J., joined by Fay and Hill, JJ.); id. at 1288-1291 (opinion of Hill, J.), and although some believed that no remand was necessary in this case, id. at 1281-1285 (opinion of Johnson, J., joined by Anderson, J.); id. at 1285-1288 (opinion of Roney, J., joined by Fay and Hill, JJ.); id. at 1288-1291 (opinion of Hill, J.), a majority of the judges of the en banc court agreed that the case should be remanded for application of the newly announced standards. Summarily rejecting respondent's claims other than ineffectiveness of counsel, the court accordingly reversed the judgment of the District Court and remanded the case. On remand, the court finally ruled, the state trial judge's testimony, though admissible "to the extent that it contains personal knowledge of historical facts or expert opinion," was not to be considered admitted into evidence to explain the judge's mental processes in reaching his sentencing decision. Id. at 1262-1263; see Fayerweather v. Ritch, 195 U. S. 276, 195 U. S. 306 -307 (1904).
D
Petitioners, who are officials of the State of Florida, filed a petition for a writ of certiorari seeking review of the decision of the Court of Appeals. The petition presents a type of Sixth Amendment claim that this Court has not previously considered in any generality. The Court has considered Sixth Amendment claims based on actual or constructive denial of the assistance of counsel altogether, as well as claims based on state interference with the ability of counsel to render effective assistance to the accused. E.g., United States v. Cronic, ante p. 466 U. S. 648. With the exception of Cuyler v. Sullivan, 446 U. S. 335 (1980), however, which involved a claim that counsel's assistance was rendered ineffective by a conflict of interest, the Court has never directly and fully addressed a claim of "actual ineffectiveness" of counsel's assistance in a case going to trial. Cf. United States v. Agurs, 427 U. S. 97, 427 U. S. 102, n. 5 (1976).
In assessing attorney performance, all the Federal Courts of Appeals and all but a few state courts have now adopted the "reasonably effective assistance" standard in one formulation or another. See Trapnell v. United States, 725 F.2d 149, 151-152 (CA2 1983); App. B to Brief for United States in United States v. Cronic, O.T. 1983, No. 82-660, pp. 3a-6a; Sarno, Modern Status of Rules and Standards in State Courts as to Adequacy of Defense Counsel's Representation of Criminal Client, 2 A.L.R. 4th 99-157, §§ 7-10 (1980). Yet this Court has not had occasion squarely to decide whether that is the proper standard. With respect to the prejudice that a defendant must show from deficient attorney performance, the lower courts have adopted tests that purport to differ in more than formulation. See App. C to Brief for United States in United States v. Cronic, supra, at 7a-10a; Sarno, supra, at 83-99, § 6. In particular, the Court of Appeals in this case expressly rejected the prejudice standard articulated by Judge Leventhal in his plurality opinion in United States v. Decoster, 199 U.S.App.D.C. 359, 371, 374-375, 624 F.2d 196, 208, 211-212 (en banc), cert. denied, 444 U.S. 944 (1979), and adopted by the State of Florida in Knight v. State, 394 So.2d at 1001, a standard that requires a showing that specified deficient conduct of counsel was likely to have affected the outcome of the proceeding. 693 F.2d at 1261-1262.
For these reasons, we granted certiorari to consider the standards by which to judge a contention that the Constitution requires that a criminal judgment be overturned because of the actual ineffective assistance of counsel. 462 U.S. 1105 (1983). We agree with the Court of Appeals that the exhaustion rule requiring dismissal of mixed petitions, though to be strictly enforced, is not jurisdictional. See Rose v. Lundy, 455 U.S. at 455 U. S. 515 -520. We therefore address the merits of the constitutional issue.
II
In a long line of cases that includes Powell v. Alabama, 287 U. S. 45 (1932), Johnson v. Zerbst, 304 U. S. 458 (1938), and Gideon v. Wainwright, 372 U. S. 335 (1963), this Court has recognized that the Sixth Amendment right to counsel exists, and is needed, in order to protect the fundamental right to a fair trial. The Constitution guarantees a fair trial through the Due Process Clauses, but it defines the basic elements of a fair trial largely through the several provisions of the Sixth Amendment, including the Counsel Clause:
In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defence.
Thus, a fair trial is one in which evidence subject to adversarial testing is presented to an impartial tribunal for resolution of issues defined in advance of the proceeding. The right to counsel plays a crucial role in the adversarial system embodied in the Sixth Amendment, since access to counsel's skill and knowledge is necessary to accord defendants the "ample opportunity to meet the case of the prosecution" to which they are entitled. Adams v. United States ex rel. McCann, 317 U. S. 269, 317 U. S. 275, 317 U. S. 276 (1942); see Powell v. Alabama, supra, at 287 U. S. 68 -69.
Because of the vital importance of counsel's assistance, this Court has held that, with certain exceptions, a person accused of a federal or state crime has the right to have counsel appointed if retained counsel cannot be obtained. See Algersinger v. Hamlin, 407 U. S. 25 (1972); Gideon v. Wainwright, supra; Johnson v. Zerbst, supra. That a person who happens to be a lawyer is present at trial alongside the accused, however, is not enough to satisfy the constitutional command. The Sixth Amendment recognizes the right to the assistance of counsel because it envisions counsel's playing a role that is critical to the ability of the adversarial system to produce just results. An accused is entitled to be assisted by an attorney, whether retained or appointed, who plays the role necessary to ensure that the trial is fair.
For that reason, the Court has recognized that "the right to counsel is the right to the effective assistance of counsel." McMann v. Richardson, 397 U. S. 759, 397 U. S. 771, n. 14 (1970). Government violates the right to effective assistance when it interferes in certain ways with the ability of counsel to make independent decisions about how to conduct the defense. See, e.g., Geders v. United States, 425 U. S. 80 (1976) (bar on attorney-client consultation during overnight recess); Herring v. New York, 422 U. S. 853 (1975) (bar on summation at bench trial); Brooks v. Tennessee, 406 U. S. 605, 406 U. S. 612 -613 (1972) (requirement that defendant be first defense witness); Ferguson v. Georgia, 365 U. S. 570, 365 U. S. 593 -596 (1961) (bar on direct examination of defendant). Counsel, however, can also deprive a defendant of the right to effective assistance, simply by failing to render "adequate legal assistance," Cuyler v. Sullivan, 446 U.S. at 446 U. S. 344. Id. at 446 U. S. 345 -350 (actual conflict of interest adversely affecting lawyer's performance renders assistance ineffective).
The Court has not elaborated on the meaning of the constitutional requirement of effective assistance in the latter class of cases -that is, those presenting claims of "actual ineffectiveness." In giving meaning to the requirement, however, we must take its purpose -to ensure a fair trial -as the guide. The benchmark for judging any claim of ineffectiveness must be whether counsel's conduct so undermined the proper functioning of the adversarial process that the trial cannot be relied on as having produced a just result.
The same principle applies to a capital sentencing proceeding such as that provided by Florida law. We need not consider the role of counsel in an ordinary sentencing, which may involve informal proceedings and standardless discretion in the sentencer, and hence may require a different approach to the definition of constitutionally effective assistance. A capital sentencing proceeding like the one involved in this case, however, is sufficiently like a trial in its adversarial format and in the existence of standards for decision, See Barclay v. Florida, 463 U. S. 939, 463 U. S. 952 -954 (1983); Bullington v. Missouri, 451 U. S. 430 (1981), that counsel's role in the proceeding is comparable to counsel's role at trial -to ensur