The Opinion of the Court was delivered by
*329LONG, J.A grand jury indicted Roy R. Williams, Jr., an off-duty police officer, for firing his service revolver at the automobile of another driver with whom he claimed to have been in a motor vehicle accident. The charges were second-degree possession of a weapon for an unlawful purpose, in violation of N.J.S.A. 2C:39-4a (Count One); fourth-degree aggravated assault by knowingly pointing a firearm at another person, under circumstances manifesting extreme indifference to human life in violation of N.J.S.A. 2C:12-1b(4) (Count Two); second-degree aggravated assault by purposely attempting to cause serious bodily injury to another person, in violation of N.J.S.A. 2C:12-1b(1) (Count Three); and attempted murder, in violation of N.J.S.A. 2C:5-1, 2C:11-3 (Count Four). Tried to a jury, Williams was acquitted on Counts Three and Four, but convicted on Counts One and Two.
The trial court sentenced Williams to a five-year custodial term with three years of parole ineligibility on the conviction for possession of a weapon for an unlawful purpose and to a concurrent eighteen-month custodial term on the conviction for aggravated assault.
Williams appealed, raising a series of issues including prosecutorial misconduct, erroneous evidential admissions, and an inadequate jury instruction on the possession of a weapon for an unlawful purpose count. His conviction was affirmed in an unpublished opinion, although the Appellate Division was divided over the sufficiency of the jury instruction.
The majority determined that the instruction adequately identified the unlawful purpose with which Williams was alleged to have possessed the firearm. In a dissenting opinion, Judge Weeker disagreed, finding that although the evidence presented at trial was sufficient to support Williams’s conviction, the inadequacy of the trial court’s instruction allowed the jury to convict him without finding, beyond a reasonable doubt, that he had the purpose to use his gun unlawfully against another. The dissent identified four errors with respect to the trial court’s instruction: (1) failure to *330define the “specific unlawful purpose”; (2) failure to relate the aileged unlawful purpose to the evidence; (3) failure to focus on the time when Williams’s possession changed from lawful to unlawful; and (4) failure to instruct that Williams’s “purpose” was to be determined by his subjective state of mind.
The case is before us as of right by virtue of the Appellate Division dissent on the issue of the adequacy of the jury instruction regarding possession of a weapon for an unlawful purpose.
I
The following evidence was adduced at trial. On June 22, 1995, Williams was involved in what he characterized as a hit-and-run accident between Tammy Erickson in one vehicle and Williams, his wife, and son in the other. At the time of the accident, Mrs. Williams was driving because Williams, who had been injured on the job a week earlier, was taking pain medication and was unable to drive. According to the Williamses, their mini-van was rear-ended by Erickson while stopped at a traffic light. When Erickson failed to pull over to exchange insurance information, Mrs. Williams pursued the fleeing vehicle, sounding her horn and flashing her headlights. At one point during the chase, Williams lost sight of Erickson’s vehicle, but shortly after spotted it and attempted to block the roadway to prevent Erickson’s escape.
What occurred next was the subject of much dispute at trial. The defense theory, as developed through the testimony of the Williamses, was that after stopping the van in the roadway Mrs. Williams proceeded to get out. Williams also exited the van with badge in hand identifying himself as a police officer. According to their testimony, it was at that point that Erickson’s vehicle, traveling at a high rate of speed, headed straight toward the side of the van where Mrs. Williams was standing. Mrs. Williams testified that she yelled for her husband and, as she was jumping out of the way of Erickson’s vehicle, she hit the door on the back side of the van. When Williams observed Erickson’s vehicle headed in the direction of his wife, he dropped his badge and *331reached for his service revolver, which he legally carried “in a gunnysack” attached to his waist. Williams claimed that he fired one round in the direction of Erickson’s passing vehicle after hearing his wife’s screams because he believed she was in imminent danger of being hit.
Williams testified that he fired his gun as Erickson’s car passed him, within a “split second” of hearing his wife scream his name. In response to the question from the assistant prosecutor, “What were you aiming at?” Williams answered: “I just fired, sir.” When asked whether he wanted to fire a shot at the person who might have just run over his wife, Williams said: “I just fired at the car in defense of my wife, sir.” In response to repeated questions with respect to the order of events surrounding the firing, Williams answered “My wife screamed and I fired in response to that.” “I fired in response to my wife’s screams, sir.” “In my mind, my wife’s life was in danger.” “I fired because Sandy was in imminent danger of being struck by that vehicle.” “I fired in response to my wife screaming and the car was passing.” The bullet hit the rear windshield of Erickson’s vehicle and exited through the front windshield without striking Erickson.
Erickson’s version of the events leading up to the shooting was in stark contrast. She denied having been involved in any collision with the Williams’ ear on June 22,1995, inferentially suggesting that she had been the victim of an unprovoked attack by Williams. She testified that while driving to work she observed a van stopped in a “weird spot” in the roadway. She then saw a man next to the van pointing a gun in her direction, at which time she hit the accelerator and turned the corner. The bullet struck her windshield. Erickson testified that the woman in the Williams’ van did not get out. Erickson telephoned police upon reaching the diner where she was employed as a waitress.
The State also presented four eyewitnesses whose testimony substantially corroborated Erickson’s claim that there were no other persons physically present in the street when Williams fired his weapon. On cross-examination the defense challenged the *332ability of those witnesses to observe what occurred from their respective locations and also questioned the point at which then* attention was first drawn to the events at issue here. On that evidence, the jury convicted Williams as outlined above.
II
Williams’s essential claim at trial was that he acted in defense of his wife in firing his service revolver. That claim, if proven, had two possible effects: to exculpate him altogether on the substantive charges of attempted murder and aggravated assault on a justification theory,1 and to provide a “failure of proof’ defense to the charge that he possessed the weapon for an unlawful purpose. See, e.g., State v. Bowens, 108 N.J. 622, 633-35, 532 A.2d 215 (1987) (holding in context of murder charge that reasonableness of defendant’s conduct bears on whether essential elements of Code offense have been met). Those are two entirely distinct uses of Williams’s defense of another evidence.
A
In order to exculpate him on the substantive charges of attempted murder and aggravated assault, Williams’s belief in the need to use force to defend his wife had to be “reasonable.” Although the Code, as originally drafted, approached justification in terms of the subjective attitudes of the criminal actor, on adoption by the Legislature, it was modified to codify the preCode common law objective standard of self-defense. Id. at 629, 532 A.2d 215; N.J.S.A. 2C:3-4a, -5a. Under that standard a jury must find that a defendant’s belief in the need for force is *333reasonable in order to excuse him from liability for a crime whose elements the State has proved. Ibid. Thus, if the jury found that Williams’s belief in the need to use force against Erickson to protect his wife was honest but unreasonable, he could not have been excused from liability for the substantive offenses of attempted murder and aggravated assault.
B
The “failure of proof’ defense advanced with respect to possession of a weapon for an unlawful purpose is entirely different. Unlike traditional notions of “self-defense,” it does not exonerate a defendant who, based on the State’s proofs, committed an illegal act. State v. Harmon, 104 N.J. 189, 207, 516 A.2d 1047 (1986). On the contrary, it admits evidence to defeat the State’s proof of the elements of the offense in the first instance. Ibid. In this ease, those elements are:
(1) the item possessed was a “firearm” within the meaning of N.J.S.A. 2C:39-1(f);
(2) the defendant “possessed” it, which under N.J.S.A. 2C:2-1(c) requires knowledge or awareness of his control over the item; (3) the defendant’s purpose or conscious objective was to use it against the person or property of another; and (4) the defendant intended to use it in a manner that was proscribed by law.
[Id. at 212, 516 A.2d 1047.]
The fourth element is pivotal here. It requires a finding that a defendant armed himself “with the actual purpose of using the weapon against another in a criminal manner.” Id. at 204, 516 A.2d 1047. Because N.J.S.A. 2C:39-4a is directed at penalizing the intent to use a weapon affirmatively to commit a crime, id. at 199, 516 A.2d 1047, the focus is on the subjective attitude of the accused. The State must prove beyond a reasonable doubt that the accused intended to use the weapon unlawfully. Where, as here, state of mind is an essential or material element of the offense, a defendant may not be deprived of the opportunity to assert a mistaken belief that could negate the mental state required to convict. Indeed, the Sixth Amendment affords a defendant that right. State v. Sexton, 160 N.J. 93, 104-05, 733 A.2d 1125 (1999).
*334We agree entirely with the dissenters that if the jury found that Williams’s belief in the need to use force in defense of his wife was honest but unreasonable, that belief could not serve to exonerate him of attempted murder and aggravated assault because we do not recognize “imperfect self-defense” in this State. State v. Branch, 155 N.J. 317, 329, 714 A.2d 918 (1998). But nothing in that conclusion eliminates the right of a defendant like Williams to challenge the proofs advanced on the State’s case in chief by showing that he lacked the intention to use his weapon unlawfully. He had a right to show that he, in fact, was motivated by an honestly held but unreasonable belief that such force was required to protect his wife. It simply does not follow that because Williams’s honest but unreasonable belief could not exonerate him of attempted murder and aggravated assault, it did not bear on the State’s burden to prove that he intended to use his weapon unlawfully.
The dissenters’ suggestion that this opinion legitimatizes imperfect self-defense is wide of the mark. Post at 338, 774 A2d at 466. Indeed, it misconceives the notion of “imperfect self-defense.” Evidence of self-defense (or defense of another) is admissible as an affirmative defense under the New Jersey Code of Criminal Justice. Harmon, supra, 104 N.J. at 206, 516 A.2d 1047; N.J.S.A. 2C:3-4, -5. It can excuse a defendant from responsibility for a crime that the State has proved against him only if certain statutory requirements are met. Those requirements are that the defendant honestly and reasonably believed that the use of defensive force was necessary. State v. Hines, 303 N.J.Super. 311, 323, 696 A.2d 780 (App.Div.1997); N.J.S.A. 2C:3-4, -5. What makes defensive evidence “imperfect” is its failure to satisfy all of the requirements the Legislature established for its potential use as an affirmative defense. Thus, if a defendant was not reasonable in believing in the need to use defensive force, he could not invoke the affirmative defense of justification because his evidence would be “imperfect” for that purpose. Such evidence would not be “imperfect,” however, if it were used for another purpose for *335which the Legislature had not established both the honest and reasonable requirements. Thus, as bearing on the State’s proof of the mental element of N.J.S.A. 2C:39-4a in its case in chief, evidence that a defendant honestly but unreasonably believed in the need to use defensive force is plainly admissible. As we explained in Harmon, swpra, “[i]f an individual’s possession of a firearm is motivated honestly by a self-protective purpose, then his conscious object and design may remain not to do an unlawful act, and a material element of a 39-4(a) violation has not been met.” 104 N.J. at 207, 516 A.2d 1047.
In sum, the dissenters’ view flows from a failure to acknowledge the well-established distinction between
a defense based on the existence of a fact that negates an essential element of the crime as defined, and the narrower concept of an affirmative defense that excuses conduct that is otherwise unlawful. See, e.g., State v. Bess, 53 N.J. 10, 16-17, 247 A.2d 669 (1968) (drawing distinction under pre-Code law between objective justification of self defense that might excuse second-degree murder and subjective intentions of self defense that could negate premeditation and deliberation required for first-degree murder). Obviously, these considerations cannot be separated in law any more than they can in life. , It is inevitable that in many cases the reasonableness of the defendant’s conduct will be presented to the jury in defense of the substantive crimes charged. Hence, any use of a firearm may involve consideration of those limited circumstances in which the use of deadly force is justifiable and may resolve the question whether the purpose was to commit an act proscribed by law.
[Harmon, supra, 104 N.J. at 209, 516 A.2d 1047 (emphasis added).]
Although an honest but unreasonable belief in the need to use force for protective purposes would not serve to exonerate Williams from the substantive charges of attempted murder and aggravated assault because of the Code’s interdiction against “imperfect self-defense,” the use of such evidence for a different purpose altogether, that is, to controvert the State’s proof of the intent element of N.J.S.A. 2C:39-4a is entirely proper and indeed unremarkable. That is the backdrop on which the jury charge must be evaluated.
Ill
Because Williams did not object to the court’s instruction at trial, the standard of review is plain error. R. 1:7-2. Under *336that standard, a defendant not only must demonstrate that the instruction was flawed, but also that in the circumstances presented “the error possessed a clear capacity for producing an unjust result.” State v. Melvin, 65 N.J. 1, 18, 319 A.2d 450 (1974); R. 2:10-2. The possibility of an unjust result must be “sufficient to raise a reasonable doubt as to whether the error led the jury to a result it otherwise might not have reached.” State v. Macon, 57 N.J. 325, 336, 273 A.2d 1 (1971). We conclude that Williams has satisfied the plain error standard in connection with the jury instruction.
TV
After giving preliminary instructions, the trial court charged the jury concerning each of the four offenses in the indictment. Second-degree possession of a weapon for an unlawful purpose was the first offense addressed by the court. On the critical element of whether Williams intended to use the gun illegally, the court stated:
The fourth element that the State must prove beyond a reasonable doubt is that the Defendant had a purpose to use the firearm in a manner that was prohibited by law.
I have already defined purpose for you.
The mental element of purpose to use a firearm unlawfully requires that you find that the Defendant possessed the firearm with the conscious objective, design, or specific intent to use it against the person or property of another in an unlawful manner, as charged in the Indictment, and not for some other purpose.
In this case, the State contends that the Defendant’s unlawful purpose in possessing the firearm was to use it unlawfully against the person of Tammy Erickson.
You must not consider your own notions of the unlawfulness of some other undescribed purpose of the Defendant, but, rather, you must consider whether the State has proven the specific unlawful purpose charges [sic].
The State need not prove which specific completed crime the Defendant intended to commit using the firearm.
The unlawful purpose alleged by the State may be inferred from all of what was said and done and from all of the surrounding circumstances in this case.
Any lawful purpose would be a defense to the charge. For example, if the Defendant believed his purpose ivas to lawfully use the firearm to protect himself or another against the use of unlawful force, then the Defendant’s conscious object *337 and design was not to use the firearm in an unlawful manner, and the State has failed to carry its burden of proof on this element beyond a reasonable doubt.
If you are satisfied beyond a reasonable doubt that the State has proven each of the elements in this offense as I have defined them, then you must find the Defendant guilty.
If, on the other hand, you find that the State has failed to prove beyond a reasonable doubt any one of the elements of this offense as I have defined them, then you must find the Defendant not guilty.
[Emphasis added.]
The trial court then went on to instruct the jury on the elements of aggravated assault and attempted murder. Immediately after completing those instructions, the trial court turned to Williams’s claim that he should be exonerated of aggravated assault and attempted murder because he acted in defense of his wife. The court was careful to point out that a requisite element of that defense is a “reasonable belief’ on the part of defendant that he had to use deadly force to defend against the conduct of another:
[Y]ou must first determine whether the Defendant used deadly force. If you find the Defendant did so, then you must determine if the Defendant reasonably believed that he had to use deadly force to defend against the conduct of another. I’ll read that again.
If you find the Defendant did so, you must determine if the Defendant reasonably believed he had to use deadly force to defend against the unlawful conduct of another. A reasonable belief is one which would be held by a person of ordinary prudence and intelligence situated as this Defendant was.
Self-defense exonerates a person who uses force in the reasonable belief that such action was necessary to prevent his death or serious injury, even though his belief was later proven mistaken.
Accordingly, the law requires only a reasonable, not necessarily a correct, judgment.
[Emphasis added.]
Following that instruction, the jury was excused to commence deliberations.
Approximately ninety minutes later, the jurors sent out the following request for clarification:
Please re-read self-defense clause and how it pertains to the third party protection, and please re-read or explain the four criteria that need to exist to find someone guilty of the first charge on our jury sheet [possession of a weapon for an unlawful purpose].
*338With no objection from counsel, the trial court simply re-read the justification instruction on defense of another which contains five separate references to the requirement of reasonableness. The court then repeated the charge on possession of a weapon for an unlawful purpose, without informing the jury that an honest but unreasonable belief concerning the need to use the weapon could be considered by the jury in evaluating whether the State proved that Williams intended to use the weapon unlawfully.
The jury’s questions highlight the potential for confusion that arises when a justification defense such as self-defense or defense of another is at issue in a case in which a defendant is also charged with possession of a weapon for an unlawful purpose. See State v. Bilek, 308 N.J.Super. 1, 8, 705 A.2d 366 (App.Div.1998) (noting that where self-defense principles are intertwined with possessory offense charge jurors may be misled into focusing on whether defendant was justified in his conduct, rather than on whether he was affirmatively acting -with criminal purpose). It is not only possible, but likely, because of the juxtaposition of the jury instruction and re-instruction, that the jury improperly imported the reasonableness requirement from the justification defense to the determination of whether Williams had the requisite state of mind to be convicted under N.J.S.A. 2C:39-4a. In other words, on this record, it is impossible to know whether the jury convicted Williams because it concluded that he was not acting in defense of his wife at all, or because it concluded that he was unreasonable in believing that there was a need to use force on her behalf.
The court was required to explain to the jury that in order to negate the unlawful purpose element of the possession offense, Williams’s belief in his need to fire the gun did not need to be reasonable, as is required to establish a justification defense to the substantive charges. To be sure, the court correctly instructed the jury regarding the justification defense. However, it was the entirely proper emphasis on reasonableness in that charge that *339contributed to the prejudice resulting from insufficient instruction on the possession charge.
Irrespective of Williams’s failure to request it, the court should have instructed the jury that even if it found his explanation — that he fired his gun to stop Erickson from killing his wife — to be unreasonable, it nevertheless had to consider whether that belief was an honestly held one. If it was, the jury could have acquitted Williams of the possessory weapons’ offense because he lacked the requisite mental state: a purpose to use the gun unlawfully. By failing to explain that a reasonable belief in the need to defend another is required for justification, but that only an honest, though unreasonable, belief is sufficient to negate a purposeful mental state, the judge left the jury to speculate about the applicable law.
Accordingly, because the charge had the clear capacity to mislead the jury, we reverse Williams’s conviction under N.J.S.A. 2C:39-4a and remand the case for a new trial. Further, we refer the issue of the jury instruction to be used in those circumstances to the Supreme Court Committee on Model Jury Charges (Criminal). Its mission will be to develop an instruction that distinguishes between the mental state required for justification (an honest and reasonable belief) and that required to negate an element of the crime (an honest but not necessarily reasonable belief) for use in cases such as the one before us.
V
Our ruling makes it unnecessary for us to grapple with the other jury instruction issues raised by the defense and in the dissent. However, we choose to make the following comments. The trial court did not adequately define what specific unlawful purpose, if any, Williams harbored when he shot at Erickson. The sole instruction in this connection was as follows: “In this case, the State contends that the Defendant’s unlawful purpose in possessing the firearm was to use it unlawfully against the person of Tammy Erickson.”
*340That charge was inadequate to meet the requirement of State v. Petties, 139 N.J. 310, 321, 654 A.2d 979 (1995), that the court properly guide the jury by relating the law to the facts. It also violated the rule enunciated in State v. Jenkins, 234 N.J.Super. 311, 316, 560 A.2d 1240 (App.Div.1989), that “a jury instruction on a charge of gun possession for unlawful purpose must include an identification of such unlawful purposes as may be suggested by the evidence and an instruction that the jury may not convict based on their own notion pf the unlawfulness of some other undescribed purpose.” The trial court adhered to the latter portion of that instruction, but not the former, and did not clearly identify “such unlawful purposes as [might have been] suggested by the evidence” so as to avoid the possibility that the jury would convict based upon impermissible considerations. Ibid.
Although the jury is permitted to infer an unlawful purpose from circumstantial as well as direct evidence, Petties, supra, 139 N.J. at 316, 654 A.2d 979, such an inference is not compelled, and, in fact, may be countered by other evidence regarding a defendant’s actual state of mind. “Thus one may at once be guilty of an aggravated assault through pointing a weapon at another yet be innocent of possession of the weapon for an unlawful purpose.” Harmon, supra, 104 N.J. at 205, 516 A.2d 1047 (citing State v. Mieles, 199 N.J.Super. 29, 488 A.2d 235 (App.Div.), certif. denied, 101 N.J. 265, 501 A.2d 933 (1985)). Just as lawful use of a weapon will not necessarily legitimate prior possession for an illegal purpose, illegal use of a weapon alone does not establish the necessary mental element under that statute. “The issue of unlawful possession turns on ‘the purpose for which defendant possessed the gun and not how he used it.’” State v. Blanks, 313 N.J.Super. 55, 73, 712 A.2d 698 (App.Div.1998) (quoting Mieles, supra, 199 N.J.Super. at 41, 488 A.2d 235) (emphasis added). Thus, contrary to the dissenters’ view, post at 338 (op. at 466-467), the mere fact that Williams was charged with and convicted of an offense stemming from use of the weapon does *341not supply the unlawful motive and is not a substitute for a proper charge.
The trial court’s obligation is to identify the unlawful purpose(s) that may be suggested by the evidence. See, e.g., State v. Diaz, 144 N.J. 628, 640, 677 A.2d 1120 (1996); Petties, supra, 139 N.J. at 319-21, 654 A.2d 979; State v. Johnson, 287 N.J.Super. 247, 263, 670 A.2d 1100 (App.Div.), certif. denied, 144 N.J. 587, 677 A.2d 759 (1996); State v. Williams, 213 N.J.Super. 30, 36-37, 516 A.2d 265 (App.Div.1986), certif. denied, 107 N.J. 104, 526 A.2d 177 (1987). Where, as here, the original possession was undisputedly lawful, the court has a special obligation to relate the alleged unlawful purpose to the evidence. State v. Villar, 150 N.J. 503, 511, 696 A.2d 674 (1997).
Although it is well-established that the trial court is not required in every case “to define with precision the exact elements of the crime the defendant is alleged to have intended to commit with the firearm,” State v. Mello, 297 N.J.Super. 452, 465, 688 A.2d 622 (App.Div.1997), that is not a license to omit any explanation of defendant’s putative unlawful purpose. At a minimum; the instruction should have included a more specific reference to the underlying substantive charges, even if only generically. Id. at 466, 688 A.2d 622. To be sure, neither acquittal nor conviction of the substantive offense is determinative of a charge of unlawful possession. Nevertheless, the other offenses charged provided at least a framework for the jury in analyzing the charge of possession of a weapon for an unlawful purpose. On the retrial, the instruction should be focused on the unlawful purpose Williams is alleged to have harbored when he shot at Erickson’s car and the jury should be instructed that Williams’s failure to comply with any internal rules and regulations of his employer do not constitute an unlawful purpose under N.J.S.A. 2C:39-4.
VI
The judgment of conviction entered upon the jury verdict is reversed. The matter is remanded for trial at which instructions *342should be tailored to the principles to which we have adverted in this opinion.
The affirmative defense of justification is not relevant under N.J.S.A. 2C:39-4a. State v. Harmon, 104 N.J. 189, 207, 516 A.2d 1047 (1986). If a defendant arms himself with intent to use a weapon against another in an unlawful manner, he can not be excused from liability under N.J.S.A. 2C:39-4a because he subsequently uses the weapon for legitimate defensive purposes. Likewise, if a defendant does not have an intent to use his weapon unlawfully against another, he will not be guilty of a violation of N.J.S.A. 2C:39-4a and therefore no justification will be necessary.