[21]*21GRABER, J.
This case comes before us on automatic and direct review of judgments of conviction of aggravated murder and sentences of death. ORS 163.150(l)(f) (1987). Defendant seeks reversal of his convictions of aggravated murder. In the alternative, he asks this court to vacate his sentences of death and remand his case to the circuit court for a new penalty phase trial. Defendant also seeks reversal of his convictions of noncapital crimes.1 We affirm defendant’s convictions, vacate his sentences of death, and remand the case to the circuit court for further proceedings consistent with this opinion.
I. SUMMARY OF FACTS
Because the jury found defendant guilty, we review the facts in the light most favorable to the state. State v. King, 307 Or 332, 339, 768 P2d 391 (1989). This case involves the second defendant convicted of murdering two young German women who were on vacation in the United States. The women were hitchhiking from California to Oregon when they met defendant and David Simonsen. Witnesses testified that they saw defendant, Simonsen, and the two women together on August 31, 1988, the day that the women were murdered. Another witness saw defendant and Simonsen later that day without the two women, but with the women’s possessions. The bodies of the two women were found in a secluded spot in Coos County. They were bound and nude from the waist down and had been shot in the head at close range with a sawed-off shotgun. Simonsen confessed to having shot the women. He pleaded guilty and was sentenced to death. See State v. Simonsen, 310 Or 412, 798 P2d 241 (1990) (reviewing sentences).
The indictment against defendant contained 11 counts, including 6 counts of aggravated murder.2 The state’s [22]*22theory of the case was that defendant had ordered Simonsen to shoot the two women, or, at least, had actively participated in their deaths. The state offered evidence that defendant exercised an inordinate amount of control over Simonsen, referring to him at times as his “robot”; that defendant had made statements to other witnesses implicating himself in the murders; and that, after the murders, defendant possessed some of the victims’ property.
Defendant was convicted of four counts of aggravated murder, two counts of felony murder, two counts of conspiracy to commit murder, two counts of first degree kidnapping, and one count of being a convicted felon in possession of a firearm. In the penalty phase, the jury answered “yes” to the three questions posed by ORS 163.150(1) (1987), and the trial court entered sentences of death.3
II. GUILT PHASE ASSIGNMENTS OF ERROR
A. Motion to Dismiss Counts of Aggravated Felony Murder
Defendant first assigns as error the trial court’s failure to dismiss the aggravated murder counts that were based on a felony murder theory.4 Under ORS 163.095(2)(d), [23]*23the defendant must commit the murder “personally.” Defendant asked the trial court to remove the aggravated felony murder counts from the jury’s consideration, contending that he did not commit the murders personally, because Simonsen admitted to pulling the trigger. The trial court evidently agreed, because it granted defendant’s motion for judgments of acquittal on those counts at the end of the state’s case-in-chief. There is no error about which to complain.5
B. Sufficiency of Evidence
1. Aggravated Murder
Defendant next argues that the trial court improperly denied his motion for judgments of acquittal on all counts of aggravated murder. Defendant argues that the state did not produce sufficient evidence to permit the jury to find that he committed the crimes charged.6 Specifically, defendant asserts that he may not be convicted on entirely circumstantial evidence; that there was no evidence that he was at the [24]*24scene at the time of the murders; and that there was no evidence that he either ordered Simonsen to kill the women or actively participated in the killings.
In ruling on a challenge that the evidence of a crime is insufficient for the jury to have convicted a defendant, the relevant inquiry is whether, after viewing the evidence in the light most favorable to the state, a rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt. State v. Walton, 311 Or 223, 241, 809 P2d 81 (1991). This court has rejected defendant’s argument that evidence that is “entirely circumstantial” can never be sufficient evidence to convict. See State v. Lerch, 296 Or 377, 396, 677 P2d 678 ((1984) (“It was the intention of this court in [State v.] Krummacher[, 269 Or 125, 139, 523 P2d 1009 (1974),] to abolish any distinction between direct and circumstantial evidence as to degree of proof.”).
Defendant contends that there was no evidence that he was present at the murders. We disagree.
Defendant’s wife testified that he left home on a trip, a few days before the murders, without any possessions except a paper bag containing clothes. At 2:30 p.m. on the day of the murders, two witnesses testified that they saw defendant, Simonsen, and the two victims at a restaurant, which was a three-hour drive south of the scene of the murders. All four left the restaurant at about 3 p.m. in defendant’s pickup truck, which headed north on Highway 101. At 6:45 p.m., a police officer issued defendant a speeding ticket at a point four and one-half miles from the scene of the crimes. The officer testified that there were no women passengers in the truck, but that he saw several items that were later identified as the victims’ possessions. In addition, at the scene, criminalists found shoe prints that were similar to prints made by defendant’s shoes, tire prints similar to prints made by the tires on defendant’s truck, and fibers similar to the those in the carpet in defendant’s truck. That evidence was sufficient to permit the jury to find that defendant was at the scene of the crimes at the time of the murders.
Defendant also argues that there was insufficient evidence that he ordered Simonsen to kill the women or that he actively participated in the murders. Assuming arguendo [25]*25that either was a necessary element of any of the theories of criminal responsibility under which defendant was convicted, we disagree with defendant’s argument.
As discussed above, there was circumstantial evidence that defendant was at the scene of the crimes at the time of the murders. In addition, defendant’s cousin testified that defendant and Simonsen visited her on September 3, 1988, a few days after the murders. During that visit, defendant called Simonsen his “robot” and said that “one time he had Dave [Simonsen] take care of it and Dave went ‘boom, boom.’ ” The witness demonstrated that defendant had pretended to shoot a gun when he made that statement. Defendant also told other witnesses, shortly after the murders, that he and Simonsen had “dusted a couple of dudes,” “robbed a couple of dead niggers,” and “ma[de] headlines.” Numerous other witnesses testified that defendant exercised great control over Simonsen and that defendant sometimes referred to Simonsen as his “robot.” Defendant told witnesses that Simonsen “took care of business” for him and would do what he wanted. Finally, on the day of the murders, defendant was seen with the victims and later without the victims but with their possessions. There was sufficient evidence for the jury to find that defendant ordered Simonsen to kill the two victims or that he participated actively in the murders.
The evidence, and the reasonable inferences that the jury could have drawn from it, were sufficient to allow the jury to find defendant guilty of aggravated murder beyond a reasonable doubt. The trial court correctly denied defendant’s motion for judgments of acquittal on all counts of aggravated murder.
2. Attempted Sexual Abuse in the First Degree
Defendant assigns error to the trial court’s instructions to the jury that it could consider the crimes of attempted first degree rape and attempted first degree sexual abuse as crimes underlying both the aggravated murder theory based on concealment of the identity of the perpetrator of a separate crime, ORS 163.095(2)(e), and on the felony murder counts, ORS 163.115(l)(b).7 Defendant does not argue that the [26]*26instructions stated the law incorrectly. Rather, he argues that there was insufficient evidence to justify instructing the jury on those underlying crimes.
We need not consider whether there was sufficient evidence of attempted first degree rape, because the verdict form shows that the jury did not agree unanimously that the state had proved attempted first degree rape. The trial court instructed the jury that it must agree unanimously on all underlying crimes. It follows that the jury did not use attempted first degree rape as an underlying crime in any of defendant’s convictions. Even assuming that it was error to instruct the jury on attempted rape in the first degree, therefore, any error was harmless.
The jury did find attempted first degree sexual abuse to be an underlying crime in some of defendant’s convictions; therefore, we consider whether there was sufficient evidence of that crime. For evidence of an attempted crime to be sufficient, the evidence must permit a rational conclusion that defendant intentionally engaged in conduct that constituted a substantial step toward the commission of the charged crime. State v. Walters, 311 Or 80, 84, 804 P2d 1164, cert den_US_, 111 S Ct 2807, 115 L Ed 2d 979 (1991). To constitute a substantial step, the act must “advance the criminal purpose charged and * * * provide some verification of the existence of that purpose.” 311 Or at 85.
The pertinent statute, ORS 163.425(l)(a)(B) (1983), provided that:
“A person commits the crime of sexual abuse in the first degree when that person:
“(a) Subjects another person to sexual contact; and
<<$ * * * *
“(B) The victim is subjected to forcible compulsion by the actor * * *.”
The evidence in this case is sufficient to permit a rational conclusion that defendant intentionally engaged in conduct that constituted a substantial step toward the commission of first degree sexual abuse. The relevant evidence [27]*27includes photographs of the victims’ bodies. Their hands were bound behind their backs, and they were nude from the waist down with their pants and underpants pulled completely off one leg and down around the other ankle. The victims were lying on their backs and each had been shot in the head. A rational juror could find that defendant removed the victims’ pants or forced them to do so. Leaving the victims naked from the waist down can constitute a “substantial step” toward the commission of sexual abuse. Removing the victims’ clothing also advanced the criminal purpose of forcing sexual contact and provided verification of the existence of that purpose. There was sufficient evidence for rational jurors to infer beyond a reasonable doubt that defendant committed attempted sexual abuse. The trial court did not err in submitting that question to the jury.
C. Admission of Photographs
1. Photographs of Victims While Alive
During the guilt phase, the trial court admitted into evidence several photographs of the victims taken while they were alive. Defendant challenged the admission of those photographs in a pre-trial motion, and he renews that challenge here. He claims that the photographs were irrelevant8 and unduly prejudicial9 and that some of them were admitted pursuant to an unconstitutional statute. The trial court admitted the various photographs for different reasons.
Exhibits 38 and 39 were admitted pursuant to ORS 41.415, which provides:
“In a prosecution for any criminal homicide, a photograph of the victim while alive shall he admissible evidence when offered by the district attorney to show the general appearance and condition of the victim while alive.” (Emphasis added.)
[28]*28The district attorney offered Exhibits 38 and 39 to show the general appearance and condition of the victims while alive; each photograph showed only one of the victims.
The guilt phase of an aggravated murder trial is a “prosecution for [a] criminal homicide.” ORS 163.005, 163.095, 163.115. Defendant’s argument that the trial court should not have admitted the photographs, because they were irrelevant or unduly prejudicial, is not well taken. ORS 41.415 directs the trial court to admit such photographs in a prosecution for a criminal homicide if the district attorney offers them to show the general appearance and condition of the victims while alive. The statute, in effect, declares the photographs to be relevant and not subject to balancing under OEC 403. See State v. King, supra, 307 Or at 334-37 (the words “shall be admitted” (emphasis added) in OEC 609(1) require trial courts to admit evidence of prior convictions for the purpose of impeaching a criminal defendant without engaging in the discretionary balancing process envisioned by OEC 403).
Defendant also contends that ORS 41.415 is unconstitutional, because it violates the Eighth Amendment to the United States Constitution.10 Specifically, defendant argues that a photograph introduced pursuant to the statute in the guilt phase of the trial automatically becomes evidence that the jury can consider in the penalty phase of the trial and that such a photograph inherently is unfair to the defendant in the penalty phase.11 This court rejected the same argument in State v. Nefstad, 309 Or 523, 560, 789 P2d 1326 (1990). We are not persuaded that we should overrule Nefstad. The statute under which the trial court admitted Exhibits 38 and [29]*2939 is not unconstitutional on the theory that defendant advances.
Exhibit 37 contained a packet of six photographs that two witnesses had used to make out-of-court identifications of the two women whom they saw with defendant and Simonsen on the day of the murders. The two witnesses testified at trial and were subject to cross-examination concerning their out-of-court identifications. The state introduced the photographs during those witnesses’ testimony at trial concerning their prior out-of-court statements of identification.12
Defendant claims that the photographs in Exhibit 37 were irrelevant. Evidence that increases, even slightly, the probability of the existence of a material fact is relevant evidence. OEC 401; State v. Walton, supra, 311 Or at 232. The photographs in Exhibit 37 increased the probability that defendant was with the victims on the day of the murders. Evidence that the women whom the witnesses had seen with defendant on the day of the murders were in fact the victims was critical to placing defendant with the victims and at the scene of the murders. That was a material fact in issue. Defendant argued at trial that the state did not prove that he was ever with the victims or at the scene of the crimes.
Neither were the photographs in Exhibit 37 unduly prejudicial. All evidence presented by one party is intended to prejudice the opposing party, i.e., to increase the likelihood that the opposing party will lose the case. State v. Pinnell, 311 Or 98, 105 n 12, 806 P2d 110 (1991). The relevant inquiry is whether the evidence was unfairly prejudicial. OEC 403; State v. Smith, 310 Or 1, 20, 791 P2d 836 (1990). The trial court’s ruling is reviewed for abuse of discretion, and this court generally defers to the trial court’s decision whether the probative value of the evidence is substantially outweighed by [30]*30the potential for prejudice. State v. Rose, 311 Or 274, 291, 810 P2d 839 (1991); State v. Walton, supra, 311 Or at 234.
Defendant does not explain how the photographs unfairly prejudiced him. They were typical photographs of two women taken on a vacation and were not unusually sympathetic in nature. We find no abuse of discretion here and, thus, no error.
Exhibits 85, 87, 90, and 91 were photographs that showed the victims, while alive, with items of personal property later found in defendant’s control. Defendant claims that the photographs were irrelevant, “because it was not disputed at trial that the girls were killed or that the property was in possession of the people with whom it was found.” That argument is unpersuasive, because the state had to prove the connection between defendant and the murders, which was disputed at trial. The photographs were relevant to show that the property that witnesses saw with defendant belonged to the victims. Moreover, defendant was charged with robbing the victims as an underlying crime in some of the murder counts. That defendant was seen with the victims’ possessions is relevant to an essential element of robbery.
Defendant next argues that, even if Exhibits 85, 87, 90, and 91 were relevant, they were unfairly prejudicial. The trial court ruled that the probative value of those exhibits was not substantially outweighed by their potential for unfair prejudice. The trial court did not err in making that ruling.
In summary, the trial court did not err in admitting Exhibits 37, 38, 39, 85, 87, 90, and 91.
2. Photographs and Impressions of Defendant’s Tires
The state introduced photographs of tire prints taken of the tires on defendant’s truck and the inked impressions from those tires. The state presented evidence through Oregon State Police criminalist Michael Scanlon concerning the tire tracks found at the scene of the murders. Scanlon took photographs of the tire tracks at the scene on the day that the police found the victims’ bodies. At trial, Scanlon described the photographs taken at the scene and compared them to [31]*31photographs that he had taken of defendant’s tires and the inked impressions of those tires. He testified that the tire impressions at the scene had the same tread design, style, and pattern of wear as the tires on defendant’s truck. He also testified that the tracks at the scene were of “insufficient clarity to make a positive match” with defendant’s tires, because he could not match fine details.
Defendant contends that the photographs had no probative value, because Scanlon could not say “conclusively” that the tire tracks at the scene matched defendant’s tires. The question is not whether the evidence is “conclusive,” however, but only whether the proffered evidence has any tendency to prove or disprove a fact that is of consequence to the determination of the action. OEC 401; State v. Clowes, 310 Or 686, 691-92, 801 P2d 789 (1990).
Scanlon’s testimony that the tire impressions at the scene had the same tread design, style, and pattern of wear as the tires on defendant’s truck increased the probability that defendant’s truck had been at the scene of the murders. That defendant’s truck had been at the scene was a material fact in issue. The trial court properly admitted the evidence.
D. Trial Judge’s Demeanor
This assignment of error concerns the actions of the trial judge in regard to one witness, Dawna Urich. Urich had cohabited with defendant at one time, and they had a daughter. The state called her to testify.
During Urich’s testimony, defense counsel objected to some of the prosecutor’s questions on the grounds that the state was leading the witness and that the questions were not relevant. The trial court ruled:
“No, I think it’s relevant to an issue. I think it’s relevant to the issue of the defendant’s doing something with the witnesses that can show some evidence, some knowledge, one, and two, at this point in time I think that leading is proper with this witness. I don’t think it has happened with other witnesses and I am going to allow it with this witness at this time. I also think the evidence is relevant.”
Defense counsel made no further objections.
[32]*32The state asked another question, and Urich asked to make a statement. The trial court excused the jury to explain to the witness that she could not make a statement. The trial court then explained to defense counsel that he was allowing leading questions, because the witness was showing some hostility and being evasive,13 and also explained why he thought that the evidence was relevant. At that point, defense counsel made a new objection:
“[W]hen I made the objection on relevance as to the evidence that is coming out of this witness, when you ruled as to the relevance, Your Honor, I am sure you don’t realize you did it, but you looked right at the jury and gave great emphasis in your voice and the way you said it in saying it was relevant, and you said that three times, and I think that you have colored this evidence to the point now that the jury thinks that whatever this lady says is going to be critical to their verdict. I think you have drawn more attention to this witness and this testimony than it deserves, and also you have drawn more attention to it than anything in this trial. I was very taken back by that. I know you didn’t do it intentionally, but it was done, Your Honor, and I don’t think there is any way that you can correct that.”
Defendant renews only that complaint, but not his objections about relevance and leading questions, to this court.
Defendant contends that the inflection of the trial judge’s voice and the way that he looked at the jury made the ruling improper. The trial judge denied that he had emphasized the ruling or looked at the jury in a significant way while making the ruling. Moreover, the trial judge had instructed the jury at the beginning of the trial that it was not to place undue emphasis on, or try to surmise why he made, any ruling about the admissibility of evidence. The record does not support defendant’s contention that the trial judge unduly emphasized the evidentiary ruling.
Defendant also argues that the trial judge intimidated the witness into “say[ing] things that she would not otherwise say.” The trial judge did tell the witness, outside the presence of the jury, to tell the truth. That apparently was [33]*33a warranted admonition to this witness, because she admitted at trial that she had lied to the grand jury, and she was claiming at trial that she had not given an earlier recorded statement to a police officer, which the officer said that she had. Nothing in the record indicates that the trial judge acted in an intimidating or overbearing manner.
The record does not demonstrate that the trial judge erred in the particulars complained of in its treatment of witness Dawna Urich.
E. Instructions
1. Presence at the Scene of the Crime
The trial court refused to give defendant’s requested instructions that “mere presence at or near the scene [of the crime] is insufficient evidence upon which to base a conviction” and that “mere presence at the scene, even with knowledge of commission of the crime is not enough to make one chargeable as an accomplice.” The trial court correctly instructed the jury on what it would need to find affirmatively in order to conclude that defendant had aided and abetted in the crimes. The trial court refused to give defendant’s requested instructions about “mere presence,” because it concluded that the subject of the requested instructions was a matter for argument. Defendant challenges that refusal as erroneous.
This court rejected the same argument in State v. Nefstad, supra, 309 Or at 549-50:
“The focus of defendant Nefstad’s argument on appeal is that the jurors should have been instructed that his mere presence at the scene of the crime * * * would have been an insufficient basis for them to find him guilty on an aiding and abetting theory. Defendant Nefstad’s requested instructions, however, stated merely the converse of the instructions that were given: under the court’s instructions defendant Nefstad could not have been found guilty on an aiding-and-abetting theory unless the jury found beyond a reasonable doubt that he, with intent to promote or make easier the crimes charged, encouraged, procured, advised, or assisted by act or advice the planning or the commission [of] the crimes alleged. If the jury had concluded that defendant Nefstad merely had been present at the scene of the murder or merely had associated with defendant Miranda, it could [34]*34not have found defendant Nefstad criminally liable on an aiding-and-abetting theory under the court’s instructions. Whether the evidence was sufficient to show that defendant Nefstad encouraged, procured, assisted, or advised defendant Miranda in the commission of the crimes charged was a matter that could have been argued to the juiy. Thus no instruction by the trial court on *• * * mere presence * * * was required.”
See also Hall v. The May Dept. Stores, 292 Or 131, 143-44, 637 P2d 126 (1981) (“Ordinarily, if a jury is correctly instructed on those elements that it must find in order to reach an affirmative conclusion, a court need not go further and submit the opposing side’s version of various circumstances that would not suffice to reach the disputed conclusion.”) (emphasis in original).
Defendant asserts that his case is distinguishable from State v. Nefstad, because “only circumstantial evidence placed him at the scene.” We have rejected a categorical distinction between direct and circumstantial evidence above. 313 Or at 24. This case is not distinguishable from State v. Nefstad in any way that would require a different outcome on this point. There was no error in refusing to give the requested instructions on “mere presence.”
2. Reasonable Doubt
At the close of the guilt phase, the trial court gave this instruction about the state’s burden of proof:
“The defendant is innocent unless and until the defendant is proven guilty beyond a reasonable doubt.
“The burden is upon the State to prove the guilt of the defendant beyond a reasonable doubt as to each charged offense or lesser included offense. The defendant has no burden of proof except as to an affirmative defense.
“ ‘Reasonable doubt’ means an honest uncertainty as to the guilt of the defendant. It is based on common sense and reason. Reasonable doubt exists when, after careful and impartial consideration of all the evidence in the case, you do not feel convinced to a moral certainty that the defendant is guilty. Proof beyond a reasonable doubt is such as you would be willing to act upon in the most important of your own affairs. Reasonable doubt, though, is not every doubt, because everything depending upon moral evidence is open to some possible or imaginary doubt.”
[35]*35Defendant excepted to the use of the phrase “moral certainty.” He also excepted to the last sentence. He argued that the instruction would lead jurors to base their verdict on the perceived moral reprehensibility of defendant, rather than “dispassionately weighing the evidence” to determine whether the state had proved its case.
All but the last sentence of the disputed instruction comes from Uniform Criminal Jury Instruction 1006. The uniform instruction derives from Chief Justice Shaw’s charge to the jury in Commonwealth v. Webster, 59 Mass (5 Cush) 295, 320 (1850). Chief Justice Shaw’s charge is the basis of the reasonable doubt instruction in many jurisdictions. McCormick, Evidence 963, § 341 (3d ed 1984); Morano, A Reexamination of the Development of the Reasonable Doubt Rule, 55 BU L Rev 507, 522-23 (1975).14
The last sentence of the instruction also derives from Chief Justice Shaw’s charge. Commonwealth v. Webster, supra, 59 Mass at 320. Although some jurisdictions include that wording in their statutory definitions of reasonable doubt, see Cal Penal Code § 1096; Guam Crim Proc Code § 90.23(a); Ohio Rev Code § 2901.05(D), it is not part of Oregon’s statutes or uniform jury instructions.
Defendant asks us to declare that Oregon’s uniform jury instruction is erroneous, because it uses the term ‘ ‘moral certainty.” He asks that his conviction be reversed on the grounds that the last sentence of the instruction was erroneous and that the error prejudiced him. Defendant bases his argument on state law and the federal constitution. We first consider the argument based on state law. See Sterling v. Cupp, 290 Or 611, 614, 625 P2d 123 (1981) (state law argument considered first).
Justice Bean, writing the opinion of the court in State v. Morey, 25 Or 241, 256-57, 35 P 655 (1894), described the problems that courts had encountered in defining reasonable doubt:
[36]*36“[[Innumerable efforts have been made by the courts to define the expression ‘reasonable doubt,’ as used in the criminal law, but so far none of them have met with universal approval, or been remarkable for accuracy of expression or clearness of thought, and in many jurisdictions the courts have declined to enter into any explanation of what the term means, because it is believed the term itself is as well calculated to convey to the mind of the juror its own meaning as any definition which can be given, and that to try to give a specific meaning to the word reasonable is * * * ‘trying to count what is not number, and to measure what is not space. ’
“The utmost confusion exists in the adjudged cases in this matter of definition, and instances abound in the books where the same definition has been held error in one jurisdiction and as correct in another, and this is even true in the same state. * * * This [confusion] grows out of the inadequacy of language to make plainer, by further definition or refining, a term the meaning of which is within the comprehension of every person capable of understanding common English.”
That description of the state of the law, made nearly 100 years ago, is a remarkably apt description of its current confused state as well. See, e.g., United States v. Pepe, 501 F2d 1142, 1143-44 (10th Cir 1974) (courts must define “reasonable doubt”); United States v. Hall, 854 F2d 1036, 1037-39 (7th Cir 1988) (courts are strongly discouraged from attempting to define “reasonable doubt”); United States v. Nolasco, 926 F2d 869, 872 (9th Cir), cert den_US_, 112 S Ct 111, 116 L Ed 2d 80 (1991) (trial court has discretion to define or not to define “reasonable doubt”); People v. Hewlett, 519 NYS2d 555, 133 AD2d 417, 418 (1987) (it is reversible error to use the phrase “moral certainty”); Monk v. Zelez, 901 F2d 885, 890 (10th Cir 1990) (“moral certainty” phrase can compensate for other part of instruction that impermissibly tends to lessen the burden of proof). Here, defendant requested a similar instruction (“reasonable doubt means a doubt that is not unreasonable”) to the one that the defendant in State v. Morey attacked, and he attacks the term “moral certainty,” which the defendant in State v. Roberts, 15 Or 187, 13 P 896 (1887), specifically sought to have included in the instruction in his case.
Oregon law is clear, however, on one point. Including the term “moral certainty” in an instruction defining [37]*37reasonable doubt is not necessarily error. In State v. Robinson, 235 Or 524, 385 P2d 754 (1963), this court considered an instruction that contained the phrase, “the evidence must establish the truth of the fact to a moral certainty.” In upholding the use of that phrase, this court wrote:
“Many definitions have come before this court for review, and we have in the past honored definitions which, like the one given in this case, equate ‘reasonable doubt’ with ‘establishing the truth to a moral certainty. ’ State v. Abrams, 11 Or 169, 8 P 327; State v. Morey, 25 Or 241, 36 P 573; State v. Roberts, 15 Or 187, 13 P 896.” 235 Or at 528.
Although the term “moral certainty” is not particularly helpful to the jury, its use in the context of the instruction in this case is innocuous or, if anything, helpful to defendant. See, e.g., McBaine, “Burden of Proof: Degrees of Belief,” 32 Cal L Rev 242, 258-59 (1944) (“To use the phrase moral certainty may convey the idea to the jury that absolute certainty is required.”); Monk v. Zelez, supra, 901 F2d at 890 (use of the term “moral certainty” could mitigate impact of other wording in instruction that might have lessened the state’s burden of proof); United States v. Smaldone, 485 F2d 1333, 1348 (10th Cir 1973), cert den 416 US 936 (1974) (inclusion of the term “moral certainty” mitigated impact of otherwise suspect reasonable doubt instruction); State v. Crenshaw, 51 Ohio App 2d 163, 366 NE2d 84, 85 (1977) (“firmly convinced” is an appropriate, but lesser standard than convinced to a “moral certainty”). We do not endorse or require the use of the phrase “moral certainty,” but we adhere to the view that its use in an instruction defining reasonable doubt is not necessarily erroneous.
Defendant next challenges the instruction based on the inclusion of the last sentence, which told the jury that reasonable doubt “is not every doubt, because everything depending upon moral evidence is open to some possible or imaginary doubt.” In construing a reasonable doubt instruction, this court wrote:
“The office of the instructions to the jurors is to inform them as to the law of the case so that they will know the governing rules. When a charge to the jury is examined for error the proper inquiry is how the instruction would naturally be understood by the average people who compose juries. If the instruction is correct as to the law and is not [38]*38couched in phraseology which is, by chance, misleading, the court has committed no error in giving [the instruction].” State v. Robinson, supra, 235 Or at 527
Unless a reasonable doubt instruction misleads the jury to believe that it can convict on a lesser degree of proof than that required, the court will not find error. State v. Roberts, supra, 15 Or at 196-97. For an instruction to constitute reversible error, it must have prejudiced the defendant when the instructions are considered as a whole. State v. Brown, 310 Or 347, 356, 800 P2d 259 (1990).
Defendant claims that the last sentence of the instruction was erroneous for three reasons: It invited the jurors to base their verdict on moral standards, rather than on the evidence; it may have confused the jury; and it diluted the burden of proof. We address each of those contentions in turn.
First, reasonable jurors, hearing this instruction in context, would not base a decision on anything' other than the evidence in the case. The trial court instructed the jurors, when defining reasonable doubt, to consider all of the evidence in the case carefully and impartially. The trial court also instructed the jurors at the beginning of trial, during trial, and at the end of trial that their role was to evaluate the evidence and that they were to remain impartial and dispassionate in that task.15
[39]*39We turn next to defendant’s contention that the instruction was reversible error, because the phrase “moral evidence” may have confused the jury. Defendant contends that, “whether the ‘moral evidence’ phrase reduced the standard of reasonable doubt, or whether it was merely confusing,” its use warrants reversal. We agree that the phrase “moral evidence” is archaic and obscure,16 and we disapprove of its use. We are not persuaded that its use in this case was reversible error, however.17
An instruction that contains a confusing phrase might be reversible error if the jury were left without guidance about the proper standard to apply in deciding the case. That is not the situation here. Although the phrase “moral evidence” is confusing, the instruction as a whole informed the jury correctly about the state’s burden of proof.
Defendant argues that the phrase “reasonable doubt” is its own best explanation. Many courts, including this one, have voiced agreement with that proposition. See, e.g., State v. Robinson, supra, 235 Or at 528 (“reasonable doubt” is a term so commonly known and understood that it requires no embellishment); State of Oregon v. Monk, 199 Or 165, 193, 260 P2d 474 (1953) (quoting People v. Klein, 305 Ill 141 [, 137 NE 145 (1922),] that “[t]here is no more lucid definition of the term ‘reasonable doubt’ than the term itself’); State v. Morey, supra, 25 Or at 257 (reasonable doubt is within the comprehension of every person capable of understanding common English and further definition cannot make it plainer). If defendant is right, then the jury knew the correct burden of proof to apply when it was told that “defendant is innocent unless and until the defendant is proven guilty beyond a reasonable doubt” and that the “burden is upon the State to prove the guilt of the defendant beyond a reasonable doubt as to each charged offense or lesser included [40]*40offense” — unless the phrase “moral evidence” detracted from the correct standard.
That leads us to the inquiry whether the last sentence of the instruction could have misled the jury to convict on a lesser burden of proof. Defendant argues to this court — although he did not argue it to the trial court — that a juror hearing the phrase that everything is “open to some possible or imaginary doubt” would subject every doubt that he or she had to the question whether the doubt was imaginary. Defendant contends that “some very real doubts might be unreasonable but, at the same time, a doubt in a juror’s imagination might not be unreasonable.” We do not agree that “reasonable” doubt includes “imaginary” doubt. See State v. Morey, supra, 25 Or at 257 (a reasonable doubt is not an imaginary doubt). Although the phrase “open to some possible or imaginary doubt” is not instructive, and we discourage its use, its inclusion in this instance, in the context of the instructions as a whole, was not reversible error.
We conclude that the instruction was not reversible error under state law. That is consistent with this court’s prior decisions. See, e.g., State v. Monk, supra, 199 Or at 195 (although “[pjossibly nothing was gained by way of clarity through incorporating into the attacked instruction all of its terms,” the instruction was nonetheless adequate); State v. Morey, supra, 25 Or at 259 (upholding a reasonable doubt instruction where the disputed language was “subject to the criticism that it does not define, but needs defining,” because the instruction as a whole was not misleading).
Having determined that the instruction was not reversible error under state law, we turn to defendant’s due process argument.18 In state criminal trials, the Due Process Clause of the Fourteenth Amendment to the United States Constitution protects the accused against conviction except upon proof beyond a reasonable doubt of the facts that constitute the crime with which the accused is charged. In re Winship, 397 US 358, 90 S Ct 1068, 25 L Ed 2d 368 (1970). In Cage v. Louisiana, 498 US 39, 111 S Ct 328, 112 L Ed 2d 339 [41]*41(1990), the Supreme Court of the United States concluded that the reasonable doubt instruction in a state’s capital trial did not comply with the standard set in Winship.
The Supreme Court, in construing the instruction, considered how reasonable jurors could have understood the charge as a whole. Cage v. Louisiana, supra, 498 US at_, 111 S Ct at 329, 112 L Ed 2d at 342. The instruction equated reasonable doubt with a “grave uncertainty”, and an “actual substantial doubt” and stated that conviction required a “moral certainty” that defendant was guilty. Ibid. The Court held:
“It is plain to us that the words ‘substantial’ and ‘grave,’ as they are commonly understood, suggest a higher degree of doubt than is required for acquittal under the reasonable doubt standard. When those statements are then considered with the reference to ‘moral certainty,’ rather than evidenti-ary certainty, it becomes clear that a reasonable juror could have interpreted the instruction to allow a finding of guilt based on a degree of proof below that required by the Due Process Clause.” IbidI.19
Defendant contends that the instruction given in his case was similarly infirm. He makes the same points as he raised in arguing that the instruction was infirm under state law. The federal standard for reasonable doubt is substantially the same as our own. Thus, we find defendant’s arguments under federal law unpersuasive for the same reasons as discussed above.
Defendant makes one additional point under federal law. He asserts that Cage v. Louisiana, supra, stands for the proposition that any instruction on reasonable doubt containing the phrase “moral certainty” is erroneous per se. We disagree with his reading of Cage. There, the Court explicitly viewed the instructions as a whole. Although it disapproved the use of the phrase “moral certainty,” it found error because the trial court had used “moral certainty” in conjunction with the phrases “grave doubt” and “substantial doubt,” which suggested a higher degree of doubt than is [42]*42required for a “reasonable” doubt. We do not read Cage to suggest that every instruction containing the phrase “moral certainty” is necessarily erroneous. See, e.g., Gaskins v. McKellar, _US_, 111 S Ct 2277, 114 L Ed 2d 728 (1991) (Stevens, J., opinion on denial of certiorari) (suggesting that the flaw in the Cage instruction was the phrase “grave uncertainty”); United States v. Nolasco, supra, 926 F2d at 871 (Cage instruction erroneous, because it equated reasonable doubt with “grave uncertainty” and “actual substantial doubt”); State v. Manning, 409 SE2d 372, 374 (SC 1991), cert den_US_, 112 S Ct 1282, 117 L Ed 2d 507 (1992) (inclusion of phrase “moral certainty” is constitutional error only when combined with other terms that suggest a higher degree of doubt than that required).
We conclude that, although the disputed portion of the instruction was not informative, and we do not endorse its use in other cases, the jury could not reasonably have construed it either to decrease the state’s burden of proof or to allow the jury to base its decision on anything other than the evidence. The giving of the instruction on reasonable doubt was not reversible error.
III. PENALTY PHASE ASSIGNMENTS OF ERROR
A. Instruction on Mitigating Evidence
Defendant assigns as error the trial court’s failure to instruct the jury, during the penalty phase, that it should consider mitigating evidence about him. As the state concedes, the instructions were inadequate to comply with this court’s opinion in State v. Wagner, 309 Or 5, 14-20, 786 P2d 93, cert den_US_, 111 S Ct 212, 112 L Ed 2d 171 (1990), which was decided after the trial in this case. Therefore, we vacate defendant’s sentences of death and remand this case to the circuit court for further proceedings.
B. Evidence of Drug Dealing
Defendant objects to evidence, introduced during the penalty phase, that he possessed, used, and sold drugs. He claims that that evidence was not relevant.20 The state [43]*43responds that the evidence was relevant to the issue whether defendant would be dangerous in the future.
Witnesses testified that defendant burned people’s houses and cars, threatened them with guns, and threatened to kill them, because they had not paid their debts for purchases of drugs, had refused to purchase drugs from defendant, or had given his name to others as a drug dealer. Defendant himself admitted that he will be violent as long as he has a drug problem.
Evidence that goes to the question of defendant’s future probable violent behavior is relevant during the penalty phase. State v. Farrar, 309 Or 132, 175, 786 P2d 161, cert den_US_, 111 S Ct 212, 112 L Ed 2d 171 (1990); State v. Moen, 309 Or 45, 76, 786 P2d 111 (1990); ORS 163.150(1)(b)(B) (1987) (jury must determine whether there is a probability that the defendant will commit future criminal acts of violence constituting a continuing threat to society). The challenged evidence bore directly on the issue of future dangerousness. The trial court did not err in admitting that evidence.
C. Defendant’s Statement of Desire to Rape
During the penalty phase, a former co-worker of defendant’s testified that defendant had told him that he would like to rape a “girl,” that it was something that he had thought about, and that he thought that it would be thrilling to do it. Defendant objected at trial that that evidence was too prejudicial to be admitted. In this court, defendant also argues that the evidence was irrelevant.
Defendant’s statements were relevant, because they indicated that he may act violently toward women in the future. The trial court did not abuse its discretion in ruling that the probative value of the statements was not substantially outweighed by the potential for prejudice. Accordingly, defendant’s claim of error is not well taken.
D. Testimony about Board of Parole Practices
Defendant next argues that the trial court erred by excluding testimony from an employee of the Board of Parole concerning the Board’s legal interpretation of aggravated murder sentencing options and its view of its statutory [44]*44authority if consecutive sentences were to be imposed. The trial court did not err in excluding that evidence. It is the function of the trial court, not witnesses, to inform the jury about the law. See State v. Brown, supra, 310 Or at 355 (trial court has a statutory obligation, ORCP 59B, to state all matters of law to the jury necessary for their information in giving their verdict); State v. Nefstad, supra, 309 Or at 551 (similar).
Defendant also contends that the trial court improperly excluded evidence that the costs of administering the death penalty outweigh the costs of imprisonment for life. The trial court properly excluded that evidence, because the issue that it addressed was a matter of policy properly reserved for the legislative branch, not a jury.
IV. CONCLUSION
We have considered all of defendant’s assignments of error and supporting arguments. Any assignment or argument that we have not discussed either has been considered by this court previously and decided adversely to defendant, is unpersuasive, or is unlikely to recur on remand. We find that there was no reversible error on the assignments of error that we have not discussed.
The judgment is affirmed as to all of defendant’s convictions. The sentences of death are vacated, and the case is remanded to the circuit court for further proceedings consistent with this opinion.