This case is before this court on automatic and direct review of a judgment of conviction for aggravated murder and sentence of death, ORS 163.150(l)(f). Defendant seeks reversal of his convictions for aggravated murder and attempted aggravated murder.1 In the alternative, defendant asks this court to vacate his sentence of death. We affirm defendant’s convictions and sentence of death.
On September 20,1990, defendant entered a bank in Washington County. There were two employees of the bank present, both tellers. Defendant went directly to one teller’s area. At gunpoint, he demanded that the teller put money in a paper bag that he had brought with him to the bank. After the teller complied with defendant’s demands, defendant stepped forward to within a foot of the teller and said, “Look at me.” With the barrel of his gun within an inch or two of the teller’s forehead, defendant shot her fatally. Defendant then said to the other teller, “Come here.” That teller ducked behind a counter and ran out of the bank. As the surviving teller left the bank, defendant shot at her. The teller fled to a nearby restaurant, where she called the police. Later that day, defendant was arrested.
Defendant pleaded not guilty to charges of aggravated murder and attempted aggravated murder. Before trial, at the request of defense counsel, two separate hearings before two different circuit court judges were held to determine whether defendant was competent to stand trial.2 The *40first hearing, held in December 1990, lasted five days. At the conclusion of that hearing, a circuit court judge found that defendant was able to aid and assist in his defense. That judge said that he was “not convinced by a preponderance of the evidence that the defendant suffers from a major mental disease or defect as defined * * * in ORS 161.295.” In support of his findings, the judge noted that all of the experts who had testified “found the defendant capable of understanding the nature of the proceedings against him” and that the only evidence that defendant was “unable to assist or cooperate with counsel or to participate in his defense” was that he remained mute. The judge further found that defendant was “electively mute” and that, if he chose to remain mute during trial, his muteness would not interfere with his ability to aid and assist his lawyer. The judge explained:
“If I had found that the defendant did suffer from a , mental illness or a mental disease or defect as defined by the statute and if that resulted in him electing to remain mute, I would have found him incompetent if I determined that the muteness resulted in him being unable to adequately communicate with his counsel. But all the evidence I’ve heard in this case indicates that the defendant historically, during periods of incarceration and hospitalization and out in society, even when mute, has been quite effective in written communication.
“Additionally, he has communicated in other nonverbal ways which might be less satisfactory insofar as mounting a defense, but his written communication has, frankly, been quite good.
“If I’m wrong in my first decision and the defendant does suffer from a major mental illness, it is only substantial — it has only substantially affected his ability to communicate orally. He remains quite capable of communicating in writing, as had been demonstrated, as I said, over the years.
“Had I found the defendant to suffer from a major mental illness, I nevertheless would have been required to find him fit to proceed because the evidence is quite substantially lacking on the point of inability to communicate sufficiently to assist and to cooperate with counsel.
“For all these reasons, I find the defendant fit to proceed.”
*41On January 10,1992, after the trial judge had denied defense counsel’s motion to waive a jury trial, a matter which we discuss infra, defendant’s lawyer asked the trial judge to re-examine the question of defendant’s competency to stand trial. The trial judge agreed. He reviewed the evidence from the prior competency hearing and heard additional testimony. The trial judge concluded that defendant was able to aid and assist in his defense. In an order dated January 30, 1992, he found:
“1. That it is more probable than not that defendant has a personality disorder;
“2. That even if defendant is schizophrenic, mutism is volitional, under defendant’s control;
“3. That defendant does not meet the criteria in ORS 161.360 excluding fitness to proceed;
“4. That defendant is legally competent to stand trial.”
Defendant does not challenge either judge’s competency ruling in this court.
At trial, defendant did not contest that he had engaged in the criminal conduct. Instead, the defense relied on the affirmative defense of mental disease or defect, i.e., “guilty except for insanity,” ORS 161.295.3
A jury found defendant guilty of one count of aggravated murder and one count of attempted aggravated murder. Following the findings by the jury during the penalty phase, the trial judge entered a judgment sentencing defendant to death on the conviction for aggravated murder and to incarceration for a period of 60 months on the conviction for attempted aggravated murder.
Defendant asserts several assignments of error. Defendant first contends that the trial judge erred in refusing *42to allow his lawyer to waive defendant’s right to trial by a jury and to proceed with a bench trial because defendant was unable to waive that right himself.
Before trial, defendant’s lawyer submitted to the trial judge in defendant’s presence a written request to waive trial by a jury. The written request was signed by defendant’s lawyer, but was not signed by defendant. The trial judge asked defendant, who, as previously stated, had been found by another trial court judge to be capable of aiding and assisting in the presentation of his defense,4 if defendant had any objection to execution of the written waiver request by his lawyer on defendant’s behalf. Defendant did not respond to the trial judge’s question. The trial judge then denied the request by defendant’s lawyer to waive defendant’s right to trial by a jury.
Article I, section 11, of the Oregon Constitution provides in part:
“In all criminal prosecutions, the accused shall have the right to public trial by an impartial jury * * *; provided, however, that any accused person, in other than capital cases, and with the consent of the trial judge, may elect to waive trial by jury and consent to be tried by the judge of the court alone, such election to be in writing * * *.” (Emphasis added.)
By necessary implication, the emphasized quoted language of Article I, section 11, requires that the defendant in a capital case, such as defendant in this capital case, is to be tried only by a jury.5 Because trial by a jury is compulsory in a capital case, the trial judge did not have authority to permit defendant to waive trial by jury and to proceed in a bench trial. The trial judge, therefore, did not err in refusing to allow the written request by defendant’s lawyer to waive defendant’s right to trial by a jury.
*43Defendant next contends that the trial judge improperly excluded testimony during the guilt phase of the trial concerning the length of time that defendant would likely spend in the state hospital if he were found guilty except for insanity. During the second redirect examination of Dr. Johannsen, a psychologist called to testify on defendant’s behalf, defense counsel inquired:
“[Defense Counsel]: Based on [the prosecutor’s] last line of questioning, Dr. Johannsen, in a case like [defendant’s], if he were found guilty except for insanity, what would be the likely outcome in terms of how much time he would spend in the State Hospital?
“[Prosecutor]: Objection, that’s clearly speculative.
‘ ‘ [The Court]: Sustained. ’ ’
Although defense counsel thereafter made an offer of proof on another issue, he did not make an offer of proof on this issue.6 OEC 103(l)(b)7 provides that error may not be predicated on a ruling excluding evidence unless the substance of the evidence was made known to the court by offer of proof or was apparent from the context within which the question was asked. See State v. Busby, 315 Or 292, 298, 844 P2d 897 (1993) (discussingprinciple); State v. Olmstead, 310 Or 455, 459-60, 800 P2d 277 (1990) (same).8 The primary purpose of the offer of proof is to enable an appellate court to *44determine whether the exclusion was erroneous and, if so, harmful, i.e., whether the error affected a substantial right of the appellant. State v. Busby, supra, 315 Or at 298. Other purposes are to permit the trial judge to reconsider his or her ruling in view of the actual evidence to be offered, 1 McCormick on Evidence 195-96, § 51 (4th ed 1992), and to enable opposing counsel to take appropriate action, Christinson v. Big Stone County Co-op., 13 F3d 1178, 1180 (8th Cir 1994).
Here, the absence of an offer of proof precludes this court from evaluating whether Dr. Johannsen’s testimony was properly excluded. From this record, it is not even apparent that Dr. Johannsen would have been able to express any opinion as to how long defendant might be held at the state hospital. During earlier questioning, he acknowledged that the length of time that a patient might spend at the hospital was up to the Psychiatric Security Review Board. Moreover, not knowing what his answer would have been makes it impossible for this court to determine whether exclusion of the testimony, if it was error, was harmful error.9 As the state points out, had Dr. Johannsen said that defendant would spend significantly less time in the state hospital than he would in prison, the trial judge’s exclusion of this testimony presumably would have helped, not hurt, defendant’s case.
Defendant next claims that the trial judge “erred in limiting defense counsel’s direct examination of psychiatrist Janzer.” Specifically, defendant asserts that evidence should have been admitted that he did not respond to defense counsel’s attempt to encourage him to waive a jury trial. According to defendant:
“The trial [judge] excluded testimony by psychiatrist Janzer that defense counsel had attempted to get defendant to waive a jury trial in Janzer’s presence. The trial [judge] held that the evidence concerning the proposed jury trial waiver was irrelevant.[10] Janzer was allowed to testify about his observations of defendant’s reactions to counsel, but he was not *45allowed to mention the jury trial waiver. Defendant submits that the testimony should not have been sanitized in that manner.”
During defendant’s case-in-chief in the guilt phase of the trial, defense counsel advised the trial court that he wanted to present testimony that he had explained to defendant, in Dr. Janzer’s presence, defendant’s “options for going to trial — especially, but not limited to, the offer that the State had made to waive the death penalty if [defendant] would personally waive a jury trial”11 and that defendant’s silence under those circumstances was not to his advantage. The trial judge expressed concerns about getting into “quasi plea negotiations” and advised defense counsel that the information sought from Dr. Janzer could be obtained “without talking precisely about the fact that there was this, in essence, kind of a ‘quasi plea offer’ ” in this case.12
The court did not, as defendant asserts, exclude the reference to “jury trial waiver” because such evidence was “irrelevant.” Rather, the court directed defense counsel to use the words “[t]rial strategies that require [defendant’s] consent which would substantially minimize his potential exposure to the death penalty” in lieu of mentioning “jury trial waiver” because of concerns about getting into “quasi plea negotiations” and because of the danger of unfair prejudice to defendant and the state. The court determined that *46referring to a “jury trial waiver” might suggest that plea negotiations had occurred in this case. For example, during the offer of proof, Dr. Janzer testified that defense counsel ‘ ‘presented [defendant] with questions and a discussion of the possible legal strategies * * * of the possible advantage to [defendant] of agreeing to a trial without a jury so as to avoid the death penalty.” (Emphasis added.) A fair interpretation of the highlighted phrase is that the state had agreed not to seek the death penalty if defendant would give up his right to a jury trial, i.e., a plea bargain.
The trial court also concluded that “quasi plea offer” evidence might unfairly prejudice the state. During voir dire, some of the jurors advised the prosecutors that they thought that it was inappropriate to plea bargain, especially in cases involving serious crimes. The unfair prejudice is especially apparent in this case because, in fact, a plea offer was never extended to defendant.
Our examination of the record reveals that defense counsel questioned Dr. Janzer about the “substance of the discussion” that counsel had with defendant in Dr. Janzer’s presence, and that Dr. Janzer was allowed to explain how that evidence supported his conclusion about defendant. The trial court’s minimal sanitization of the evidence, to which defense counsel agreed (or at least to which defense counsel did not object), did not prevent defendant from questioning Dr. Janzer fully about his relevant observations. See State v. Harberts, 315 Or 408, 417-18, 848 P2d 1187 (1993) (redaction of inadmissible matters from proffered testimony may be permitted if the meaning of the remainingproffered testimony is not significantly altered).
The use by defense counsel of the words “jury trial waiver” during his questioning of Dr. Janzer might have communicated falsely to the jury that a plea offer had been extended to defendant when, in fact, no such plea offer had been made. For the foregoing reasons, we hold that the trial court did not improperly limit psychiatrist Janzer’s testimony.
Defendant also claims that the trial judge erred in excluding Dr. Johannsen’s testimony concerning whether defendant’s behavior in declining to waive a jury trial to avoid *47the death penalty was self-defeating. Defense counsel proposed to ask Dr. Johannsen the following question:
“If I told you further that it was not merely a hypothetical, but that that is, in fact, the case as indicated not only by court record but also by testimony which will be offered by Dr. Janzer who witnessed myself conducting an interview with [defendant] informing him of all the possible permutations and advising him that he had no other realistic choice, but to waive the jury in order to avoid the death penalty or to eliminate the possibility of the death penalty, * * * would your opinion be the same, that is, as it would be in the hypothetical?” (Emphasis added.)
For many of the reasons stated in our discussion of the previous assignment of error, we hold that the trial court did not err in excluding that evidence.
We have considered all of defendant’s other assignments of error and every argument in support thereof. Those same assignments of error and arguments either have been addressed previously by this court and rejected or are not well taken. Discussion of them would not benefit the bench or bar. We find no error based on those assignments of error.
The judgment of conviction for aggravated murder and attempted aggravated murder is affirmed. The sentence of death is affirmed.
ORAP 12.10(2) provides:
“If, in addition to a conviction for aggravated murder forming the basis for the death sentence, a defendant is convicted of one or more charges arising from the same charging instrument, the Supreme Court shall have jurisdiction to review any such conviction without the filing of a notice of appeal.”
ORS 161.360 provides:
“(1) If, before or during the trial in any criminal case, the court has reason to doubt the defendant’s fitness to proceed by reason of incapacity, the court may order an examination in the manner provided in ORS 161.365.
“ (2) A defendant may be found incapacitated if, as a result of mental disease or defect, the defendant is unable:
“(a) To understand the nature of the proceedings against the defendant; or
“(b) To assist and cooperate with the counsel of the defendant; or
“(c) To participate in the defense of the defendant.”
ORS 161.295 provides:
“(1) A person is guilty except for insanity if, as a result of mental disease or defect at the time of engaging in criminal conduct, the person lacks substantial capacity either to appreciate the criminality of the conduct or to conform the conduct to the requirements of law.
“(2) As used in chapter 743, Oregon Laws 1971, the terms ‘mental disease or defect’ do not include an abnormality manifested only by repeated criminal or otherwise antisocial conduct, nor do they include any abnormality constituting solely a personality disorder.”
As previously noted, defendant does not challenge the correctness of that ruling.
Article I, section 11, of the Oregon Constitution originally provided in relevant part: “In all criminal prosecutions, the accused shall have the right to public trial by an impartial jury * * Or Const, Art I, § 11 (1859). Article I, section 11, was amended by referendum in 1932 to provide explicitly that defendants in non-capital cases could waive a jury trial with the trial court’s consent and be tried before the court. Or Laws 1933 (constitutional amendments), p 5.
Although the trial judge sustained the prosecutor’s objection on the ground that defense counsel’s question called for speculative evidence, defendant does not address that issue before this court. Instead, he argues before this court that the prosecutor’s questioning on recross-examination “opened the door” to Dr. Johann-sen’s testimony. Because that ground for admission was not clearly argued in the trial court, see State v. Hitz, 307 Or 183, 188, 766 P2d 373 (1988) (positions of the parties should be clearly presented to the initial tribunal), we will not consider it.
OEC 103(1) provides in part:
“Evidential error is not presumed to be prejudicial. Error may not be predicated upon a ruling which admits or excludes evidence unless a substantial right of the party is affected, and:
<<* * * * *
“(b) In case the ruling is one excluding evidence, the substance of the evidence was made known to the court by offer or was apparent from the context within which questions were asked.”
See also State v. Affeld, 307 Or 125, 764 P2d 220 (1988) (ordinarily, when a trial court excludes testimony during direct examination or cross-examination, an offer of proof is required to preserve any claim of error related to what the evidence would have shown).
“[A] substantial right of a criminal defendant is not affected if there is * * * little likelihood that the error affected the verdict.” State v. Hansen, 304 Or 169, 180, 743 P2d 157 (1987) (citing State v. Miller, 300 Or 203, 220-21, 709 P2d 225, cert den 475 US 1141 (1985)).
As discussed infra, that argument is somewhat miscast: the trial judge did not hold that evidence concerning the proposed jury trial was irrelevant.
As stated infra, no plea offer had been extended to defendant.
Plea discussions and plea agreements are inadmissible “for or against a defendant in any criminal * * * proceeding.” ORS 135.435. That statute provides:
“(1) Except as provided in subsection (2) of this section, none of the following shall be received in evidence for or against a defendant in any criminal or civil action or administrative proceeding:
“(a) The fact that the defendant or the counsel of the defendant and the district attorney engaged in plea discussions.
“(b) The fact that the defendant or the attorney of the defendant made a plea agreement with the district attorney.
“(c) Any statement or admission made by the defendant or the attorney of the defendant to the district attorney and as a part of the plea discussion or agreement.
“(2) The provisions of subsection (1) of this section shall not apply if, subsequent to the plea discussions or plea agreement, the defendant enters a plea of guilty or no contest which is not withdrawn.”
Similarly, ORS 135.445 and OEC 410 restrict the admission of evidence concerning guilty pleas that are not accepted or are withdrawn.