¶ 55. 0concurring). I agree with the majority that Carter did not receive ineffective assistance of counsel and is therefore not entitled to a new trial. I also agree with the majority that the evidence Carter presented at the post-conviction hearing was insufficient to demonstrate that he was prejudiced by his attorney's failure to seek the admission of evidence of a prior assault.
¶ 56. I write separately, however, because the majority goes further. It unnecessarily places its imprimatur on the attorney's "strategic decision," which was apparently made in ignorance of the law and left unaddressed a question that was fundamental to the defense in this case. Because the court should not needlessly ratify this attorney's questionable decision, I respectfully concur.
I
¶ 57. In State v. Pulizzano,1 the court recognized an exception to the rape shield statute, Wis. Stat. § 972.11(2)(b). It concluded that a defendant may have a constitutional right to present evidence of a prior sexual assault to demonstrate an alternative source of the child's detailed sexual knowledge. Based on Sargent's testimony at the post-conviction hearing, the court of appeals determined that he "was unfamiliar with the Pulizzano exception to the rape shield statute." State v. Carter, No. 2008AP1185-CR, unpublished order at 4 (Wis. Ct. App. March 12, 2009). At the hearing, Sargent acknowledged that he did not "ever review a case called State v. Pulizzano”2
*680¶ 58. The majority recognizes that it need not determine whether Sargent's performance was deficient, because "even assuming that [it] was deficient, the deficiency did not prejudice Carter's defense." Majority op., ¶ 3. The majority could have and should have decided this case based solely on a determination of no prejudice. Instead, the majority unnecessarily gives Sargent's performance a stamp of approval. Despite his apparent admitted ignorance of the relevant law and the failure of his purported strategy to address a question fundamental to the defense, the majority determines that the "strategic decision. . . was objectively reasonable considering all the circumstances." Id.
A
¶ 59. Why does the majority needlessly ratify a "strategic decision" when Sargent apparently made the decision without knowing the law? The majority sets the bar too low when it relegates knowledge of the law to merely a "better practice." It cautions "that the better practice is for counsel to always research and be familiar with pertinent legal authority." Id., ¶ 34.
¶ 60. Ignorance of the relevant law is often considered deficient performance. Even the State appears to acknowledge deficient performance here. After scant *681briefing on deficiency, the State concludes: "[P]erhaps Sargent's decision not to pursue the matter further was not reasonable[.]3
¶ 61. In State v. Felton, we thoroughly considered how defense counsel's ignorance of a possible defense strategy should be evaluated in an ineffective assistance claim. 110 Wis. 2d 485, 329 N.W.2d 161 (1983). We concluded that without knowledge of the applicable law, it is impossible for an attorney to "make a reasoned decision consistent with the standard of performance expected of a prudent lawyer," and that the court should not "ratify a lawyer's decision merely by labeling it... 'a matter ... of trial strategy.'" Id. at 505-06, 502.
¶ 62. In that case, Rita Felton was routinely battered by her husband and shot him on a day when his physical abuse was especially acute. Id. at 489-92. Felton was charged with second degree murder. Id. at 488. Prior to trial, defense counsel quickly zeroed in on a theory of self-defense and therefore failed to further explore the statutes and discover an alternative defense. Id. at 505. Because counsel was ignorant of the heat-of-passion defense, "he never was in a position even to consider whether, in light of the facts, heat of passion was an appropriate defense." Id.
¶ 63. Post-conviction, the circuit court deferred to counsel's "strategic choice": "[T]here may have been some shortcomings in the matters handled during the trial, but very often that is a matter of trial strategy. . . . *682[T]he defenses [Felton's attorney] put forth were a matter of choice and of trial strategy, and not grounds for a new trial." Id. at 498.
¶ 64. On review, we acknowledged that "this court is loath to interfere with a lawyer's exercise of professional judgment by a hindsight evaluation." Id. at 507. Nevertheless, we clarified that "strategic or tactical decisions must be based upon rationality founded on the facts and the law." Id. at 502. "We will in fact second-guess a lawyer if the initial guess ... is the exercise of professional authority based upon caprice rather than upon judgment." Id. at 503.
¶ 65. We unanimously concluded that "[t]he failure to be informed of this defense in the circumstances of this case constitutes a glaring deficiency in trial counsel's knowledge of the law" and was deficient performance.4 Id. at 505. We refused to "ratify a lawyer's decision merely by labeling it, as did the trial court, 'a matter of choice and of trial strategy.'" Id. at 502.
¶ 66. Here, Sargent acknowledges that he did not make a legal determination about whether evidence of the prior assault would have been admissible. See majority op., ¶ 15. Because of his apparent ignorance of Pulizzano, it appears impossible for him to "weigh alternatives and to make a reasoned decision" consistent with professional standards. See Felton, 110 Wis. 2d at 505-06. Instead, the decision was made in a legal vacuum. I cannot join the majority in putting a *683stamp of approval on a decision apparently made in ignorance of the applicable law.
B
¶ 67. There is an additional reason that the court should not put its imprimatur on Sargent's questionable strategic decision. Sargent's purported strategy left unaddressed a fundamental question: was Cassandra telling the truth about the source of her detailed sexual knowledge?
¶ 68. At the post-conviction hearing, Sargent explained that he wanted to avoid challenging the credibility of a sympathetic five-year-old girl. Instead, he asserted, he planned to attack her mother's credibility and demonstrate that the mother pressured Cassandra into making false allegations. Majority op., ¶ 14. The majority concludes that this strategy was reasonable:
[B]y attempting to demonstrate that Cassandra gained her detailed sexual knowledge, not from Carter, but from a previous sexual assault by her cousin, Sargent would necessarily have been asking the jury to discredit the testimony of a five-year-old victim of sexual assault. It is certainly reasonable that Sargent was more confident asking the jury to discredit the mother, Denise, instead of directly attacking the child victim.
Id., ¶ 33.
¶ 69. Although it might have been worthwhile to challenge the mother's credibility, it was essential to the defense that Sargent challenge the child's credibility as well. Even if the mother had originally fabricated the story, it was the child who was repeating as true the mother's allegations. In his opening argument, Sargent argued to the jury that "there[] reallyD is no clear evidence that Michael Carter did anything improper *684towards this girl." Yet, there was such evidence— Cassandra's own testimony.5
¶ 70. If the jury fully credited this testimony, then the allegations were true and Carter was guilty. Thus, it was essential to the defense that Sargent challenge Cassandra's credibility. Unless Sargent was able to undermine her version of events, the jury would be forced to conclude that Carter did in fact do something "improper towards this girl."
¶ 71. In fact, contrary to the "strategy" he described at the post-conviction hearing, Sargent did make attempts to discredit Cassandra. Ultimately, she testified that she "want[ed] to get away from that house" and from Carter. Certainly, the jury might infer that Cassandra had a motivation to tell a story that would keep Carter away.
¶ 72. Yet, Sargent's "strategy" left unaddressed one fundamental question. How was a girl of that age able to recount a sexual incident with many sexual details had she not been assaulted by Carter?6 In Pulizzano, we explained that in the absence of evidence *685of an alternative source for a child's detailed sexual knowledge, the jury would likely make the "logical and weighty inference" that the alleged assault had occurred. 155 Wis. 2d at 652.
¶ 73. The majority's lengthy reiteration of portions of the testimony and argument is notable only for what it does not demonstrate. The record does not demonstrate that Sargent fully followed through with his "strategy" of demonstrating that the mother pressured Cassandra into making untruthful allegations. Further, Sargent never argued that the mother provided Cassandra with the necessary adult information to tell a convincing story.7 In light of these shortcomings, it is surprising that the majority concludes that Sargent's purported strategy was "reasonable under the circumstances."
II
¶ 74. Here, the majority's willingness to ratify Sargent's questionable trial strategy, which was apparently made in ignorance of the applicable law, is troublesome. Where there is ignorance of the law, you cannot excuse a lawyer's performance by labeling it trial strategy.
*686¶ 75. The majority, however, ultimately concludes that "irrespective of whether Sargent's performance was deficient, Carter's ineffectiveness claim still fails because the deficiency did not prejudice Carter's defense." Majority op., ¶ 36. I agree.
¶ 76. The law is clear that Carter is not entitled to a new trial unless he demonstrates that (1) his counsel's performance was deficient and (2) the deficiency prejudiced his defense. It is well settled that the court need not decide whether an attorney's performance was deficient if the court has already determined that there was no prejudice. Id, ¶ 21 (citing Strickland v. Washington, 466 U.S. 668, 687 (1984)).
¶ 77. To demonstrate prejudice, Carter has the burden to "show that there is a reasonable probability that, but for counsel's unprofessional errors, the result of the proceeding would have been different." Strickland, 466 U.S. at 694. In this case, that means that Carter had to show a reasonable probability that the evidence would have been admitted and would have been persuasive to the jury.8
¶ 78. I agree with the majority that the evidence Carter presented at the post-conviction hearing was insufficient to satisfy the Pulizzano test. See majority op., ¶¶ 39-53. Without showing a reasonable probability that the evidence of an alleged prior assault would have been admitted at trial, Carter has not demon*687strated that he was prejudiced by Sargent's apparent ignorance of the law. Therefore, he is not entitled to a new trial.
¶ 79. Generally, an appellate court should decide cases on the narrowest possible grounds. State v. Blalock, 150 Wis. 2d 688, 703, 442 N.W.2d 514 (Ct. App. 1989). I am at a loss to understand why the majority feels compelled to go further here. I cannot understand why it unnecessarily concludes that Sargent made a "reasonable strategic decision," even though this decision was apparently made in ignorance of the law and left unaddressed a question fundamental to the defense in this case. Accordingly, I respectfully concur.
¶ 80. I am authorized to state that Chief Justice SHIRLEY S. ABRAHAMSON joins this concurrence.
State v. Pulizzano, 155 Wis. 2d 633, 456 N.W.2d 325 (1990).
The following exchange took place between Carter's post-conviction counsel and Sargent:
*680Q: Did you ever review a case called State v. Pulizzano?
A: No, I did not.
Q: Or any subsequent case that quotes the Pulizzano test?
A: Prior to trial, no, I did not.
Q: Did you do any research that led you to any conclusion as to the admissibility of the prior incident?
A: I did not go into researching of that issue.
At oral argument, counsel for the State asserted that Sargent's strategy was reasonable. The court asked: "If he doesn't know what the facts are and he has not really carefully looked at Pulizzano, then how can he make a reasonable strategy?" The State's attorney responded, "I think I agree with that statement, that he can't."
See also State v. Thiel, 2003 WI 111, ¶ 40, 264 Wis. 2d 571, 665 N.W.2d 305 ("[D]efense counsel cannot claim to have decided strategically to forgo interviewing a particular witness if counsel has not read the police report relating to that witness, because that would not be an informed decision.").
Cassandra testified that she and Carter were sitting on the couch, that her mouth was on his private part, and that Carter was pushing on her head saying "[k]eep on going down." She testified that afterwards, she went to the bathroom to wash up because she "had some white stuff on her hand.
In closing arguments, the prosecutor repeatedly emphasized Cassandra's detailed sexual knowledge as proof of Carter's guilt. She asked the jury to consider Cassandra's "opportunity for observing and knowing the matters testified to .... And the reason I say that is, the proof is really in the pudding. The proof is in what this little girl said... . [She testified she] could see the dark hair of Mr. Carter's groin.... Now, she doesn't know why that's important. She doesn't know that men have hair there, but she observed that.... And that is something that a *685six-year-old is not gonna know." The prosecutor repeated this theme when discussing Cassandra's knowledge of erections, ejaculation, and oral sex.
As the majority reports, there was evidence that Carter and Denise had a "broken relationship." See majority op., ¶¶ 26-29. Yet Sargent never explained to the jury how the hostility in the household could be relevant in evaluating the likelihood of Carter's guilt. As the majority acknowledges, the only direct suggestion that Denise could be the ultimate source of the allegations came from the prosecutor, rather than defense counsel. See id., ¶ 30.
As we explained in Felton, "[t]here are, of course, a multitude of cases in which a lawyer's failure to inform himself of a particular defense could in no way be prejudicial[.]" 110 Wis. 2d at 507. "If the failure could have had no adverse effect on the defendant, the representation would not have been any more effective had that failure not occurred." State v. Fencl, 109 Wis. 2d 224, 241, 325 N.W.2d 703 (1982) (Heffernan, J., concurring).