(dissenting, with whom Gillerman, J., joins). The majority acknowledges that the instruction with regard to third prong malice was error because of the reference to grievous bodily harm, but concludes that there was no substantial risk of *807a miscarriage of justice, citing the strength of the Commonwealth’s case and evidence that the defendant purposefully returned to the scene with a combat knife and stabbed the victim with it. I respectfully dissent because the majority’s focus on the evidence of the defendant’s conduct attaches no importance to the evidence of his substantial impairment, that is to say his subjective understanding of what he was doing.
Where the evidence is conflicting, as it was in this case on the issue of what the defendant knew, an appellate court is prevented “from concluding that the jury were required to find a plain and strong likelihood of death.” Commonwealth v. Azar, 435 Mass. 675, 688 (2002). “It is not for us to say that one side’s evidence was more credible than the other.” Id. at 689. By placing undue emphasis on the testimony of the Commonwealth’s expert and evidence of the defendant’s conduct, the majority assumes the jury concluded that the defendant was aware he held a knife and stabbed someone with it. Although the facts would warrant such a finding, the jury could as readily have found that the impaired defendant was unaware of having held a knife or stabbed a person. “Any thought that we should disregard the error in the instructions because the evidence plainly warranted a finding of malice on [a] largely objective basis . . . has to be rejected.” Commonwealth v. Grey, 399 Mass. 469, 474 n.4 (1987).1
The issue is not whether the judge gave a correct instruction on impairment.2 Rather, the basis of my dissent is that the evidence, including the evidence of impairment, did not require the jurors to find that the defendant knew he had a knife and knew that he stabbed the victim with it. Commonwealth v. Azar, 435 Mass. 675, 688 (2002). In order to determine whether there has been a substantial risk of a miscarriage of justice, “[w]e *808review all of the evidence and the case as a whole,” Commonwealth v. Azar, 435 Mass. at 687. Where, as here, there is strong evidence of impairment affecting the defendant’s state of knowledge of the entire event, the analysis requires that we consider that evidence in determining what the jury could have concluded about the defendant’s state of knowledge. See Commonwealth v. Sama, 411 Mass. 293, 296 (1991).3
On all of the evidence, the jury could have found the following: As the result of a serious childhood automobile accident and a subsequent accident resulting in head trauma, the defendant suffered from organic brain syndrome. He functioned at a borderline level of intelligence. During the relevant time-frame, he had “an intoxicated blood level of alcohol” and was in a “severe state of intoxication.” The effect of alcohol on the defendant’s brain function would put the defendant at the time of the stabbing “in the midst of an alcoholic hallucinatory psychotic state.” In this state he had no recollection of having had a knife or of stabbing anyone. He could recall none of the events that occurred from the time he urinated at the bar until after the stabbing when he arrived at the hospital, wondering aloud why he was there. After being informed by his friend that he had been in a fight and that two or three guys had jumped him, he stated to a hospital security guard that he had been in a fight with three people, that he had been hit with a full bottle, “a third guy came at him with a knife,” and he had “decked” *809one of his assailants, thrown one against a wall and grabbed the arm of the guy with the knife “to try to stop anybody getting hurt.” He then had blacked out and was unable to “remember anything.” The defendant turned himself in when he learned, the next day, that one of his assailants had died.
In light of strong and credible evidence of the defendant’s mental impairment and severe intoxication that combined to cause memory loss and a state of hallucination, the risk is substantial that the jury found the defendant incapable of forming the intent to kill or inflict grievous bodily harm, and determined that his knowledge of the circumstances was limited to an awareness (if he had any at all4) of “decking” an assailant, throwing an assailant against the wall, and attempting to disarm one who held a knife, conduct sufficient to result in serious harm, not death.
There is additional support for the view that the jury were misled, and the conclusion that there was in this case a substantial risk of miscarriage of justice. The erroneous third prong malice instruction was repeated eight times during the charge, and the jury, indicating their confusion, asked “What are the requirements for malice aforethought?” They were again given the defective instruction. The judge also included the erroneous “grievous bodily harm” or “injury” language when he further instructed on the effects of intoxication in connection with third prong malice. There is no mistaking that the message, pervading the charge, was that the jury could convict the defendant of second degree murder on the basis of conduct that risked only grievous bodily harm.
The third prong malice instructions were also incorrect when, on three of the eight occasions in which the instruction was given, the judge instructed that malice could be inferred from the doing of an act, rather than from the defendant’s knowledge of the circumstances. For example, he said, on one such occa*810sion: “Malice aforethought also includes an unexcused . . . general intent — not specific intent — an unexcused general intent to do an act creating a plain and strong likelihood that death or grievous bodily harm would follow.” The jury were thus instructed that what the defendant actually did was sufficient to create a risk of grievous bodily harm regardless of his ability to perceive or understand what he was doing or had done. By instructing the jury that they could return a verdict of second degree murder merely upon proof that the defendant’s conduct was likely to cause grievous bodily injury, the five issue at trial was effectively eliminated from the jury’s consideration.
Further, the error in the third prong malice instruction could have been compounded by the instruction, given twice, that permitted the jurors to infer malice from the intentional use of a dangerous weapon, without more, defining dangerous weapon as “any instrument which, by its construction or its use, is capable of causing death or grievous bodily injury, or one which could be perceived by a reasonable person as being so capable.”5 Compare Commonwealth v. Farrell, 322 Mass. 606, 614-615 (1948) (defining dangerous weapon for purposes of assault and battery as “any instrument or instrumentality so constructed or so used as to be likely to produce death or great bodily harm”).6
Nor did the judge specifically instruct (he was not asked to do so) that, in determining whether the defendant intended to use a dangerous weapon, file jury should consider any credible evidence of mental impairment or intoxication. Model Jury Instructions on Homicide 61 (1999). Neither did he give any supplemental instruction that, whenever the Commonwealth must prove intent or knowledge, the jury should consider such evidence of impairment or intoxication in determining whether *811the Commonwealth has met its burden. Commonwealth v. Sires, 413 Mass. 292, 300 (1992) (“All that we have ever required be said to juries about the effect of drug consumption on a defendant’s intent or knowledge would be satisfied by a simple instruction that the jury may consider credible evidence of the effects of the defendant’s consumption of drugs in deciding whether the Commonwealth had met its burden of proving the defendant’s state of mind beyond a reasonable doubt”), citing Commonwealth v. Murphy, 426 Mass. 395, 400 (1998). See Commonwealth v. Glass, 401 Mass. 799, 810 (1988) (“A jury should not ... be foreclosed from considering the effects of voluntary consumption of alcohol on the proof of any crime which requires proof of a defendant’s specific intent”). The dangerous weapon instruction as given in this case permitted the jury to infer malice without considering whether the defendant’s impairment precluded his forming the requisite intent to use such a weapon.
For the foregoing reasons, I think the risk was substantial that the defendant was convicted on the basis of conduct, insofar as that conduct was known to the defendant, that could only have supported a conviction of manslaughter and not second degree murder. I would reverse.
“The evidence here warranted a finding of guilty of murder in the second degree. Nothing we decide today eliminates the possibility that, at a second trial, such a verdict will again be returned.” Commonwealth v. Grey, 399 Mass at 474.
Nor do I think it appropriate to consider whether the Commonwealth’s evidence is sufficient to support a conviction on the basis of the first or second prongs of malice. The jury did not specify their theory of malice, and in these circumstances we “assume, favorably to the defendant, that the guilty verdict was based on the [consideration of an incorrect instruction as to the] third prong of malice.” Commonwealth v. Delaney, 418 Mass. 658, 666-667 (1994).
Commonwealth v. Sama, supra, illustrates that the use of a knife in circumstances which, objectively, support the conclusion that the defendant was aware of his actions, is not dispositive where mental impairment may have affected the defendant’s awareness. The defendant and the victim had spent the day and evening drinking alcohol and taking drugs. There was a fight, and “the defendant used his pocket knife to slash the victim twenty-three times about the face, head, ears, and neck.” Id. at 296. The police picked up the defendant after receiving a call. He appeared intoxicated, was bloodied and crying when he asked about the charges against him, but stopped crying when informed he was only in protective custody. While in custody, he gave false statements about his activities of that day. The defendant’s expert opined that the defendant was a chronic alcoholic who on the day in question was likely intoxicated from ingesting alcohol and Xanax, would likely experience memory loss, and could have been hallucinating, although there was no evidence about the defendant’s susceptibility to hallucinations. The defendant claimed that, as a result of his intoxication, “he could not remember the killing and, in any event, he did not intend to do so;” he recalled no events between the time of the incident and when he awoke in a jail cell. Id. at 295.
Cf. Commonwealth v. Sama, 411 Mass. at 301 n.2 (“During their deliberations, the jury asked the judge to explain what he meant when he told them they could not consider the effect of the defendant’s intoxication in relation to the third prong of malice. In responding to the question, the judge suggested that the evidence of the defendant’s debilitating intoxication, if believed, would permit the jury to find that the defendant had no knowledge of the circumstances. This instruction touched on a proper statement of the law”).
Our courts have said that it is correct to instruct that “[m]alice may be inferred — it does not have to be — from the intentional use of a dangerous weapon.” Commonwealth v. Roderick, 429 Mass. 271 (1999). See also the Model Jury Instructions on Homicide 61 (1999) (“As a general rule, you are permitted to infer that a person who intentionally uses a dangerous weapon on another person is acting with malice”).
Such an instruction would permit a jury to infer malice, in the absence of evidence that the defendant intended to kill or to inflict grievous bodily harm, based on the intentional use of a weapon capable only of inflicting grievous bodily harm.