OPINION OF THE COURT
NIX, Justice.
Today we must decide whether psychiatric evidence is admissible to be evaluated by the jury when an accused offers it to negate the element of specific intent required for a conviction of murder of the first degree thereby reducing the crime to murder of the second degree.1We [213]*213are persuaded by the vast weight of authority that psychiatric evidence should be admissible for this purpose and, therefore, we hold that the learned court below erred in excluding the proffered testimony from the jury’s consideration.2
Prior to analyzing the specific facts of this case, it is necesssary to clarify what we do not decide in today’s opinion. First, appellant has not raised the defense of [214]*214insanity and today’s decision in no way affects the vitality of the M’Naghten test as the sole standard in this Commonwealth for determining criminal responsibility where the actor alleges mental illness or defect.3 Second, for reasons that will be discussed hereinafter, we do not view the position adopted today as inferentially accepting the irresistible impulse test which we have previously expressly rejected.4
5Third, we do not here reach the question of the applicability of the principles announced herein to crimes requiring a specific intent other than murder of the first degree.
Appellant, Michael Walzack, was tried before a jury and convicted of murder of the first degree in the shooting death of one Ole Toasen. Following a penalty hearing, appellant was sentenced to life imprisonment. Post-trial motions for a new trial and in arrest of judgment were filed and denied and this direct appeal followed.6
During the trial, the defense admitted the killing and attempted to establish its position through the testimony of appellant and a Dr. Willis. When called to the stand, the defense made an offer of proof indicating that the witness did not intend to contest appellant’s sanity at the time of the incident, under the M’Naghten standard. The defense conceded that appellant was sane; that he [215]*215could tell the difference between right and wrong and that he knew the nature and quality of his act. The single stated purpose in offering the witness was to demonstrate that as a result of a surgical procedure, a lobotomy, which appellant had undergone, he did not possess sufficient mental capacity to form the specific intent required for a conviction of murder of the first degree.6
In rejecting the psychiatric evidence, the trial court relied on a number of our earlier closely divided decisions. Commonwealth v. Tomlinson, 446 Pa. 241, 284 A. 2d 687 (1971) (majority opinion by Bell, C. J., concurring opinion by Barbieri, J., dissenting opinion by Roberts, J., in which Jones and Pomeroy, JJ., joined); Commonwealth v. Weinstein, 442 Pa. 70, 274 A.2d 182 (1971) (opinion in support of affirmance of judgment by Bell, [216]*216C. J., Eagen and O’Brien, JJ., concurred in the result, opinion in support of reversal of judgment by Roberts, J., in which Jones and Pomeroy, JJ., joined); Commonwealth v. Rightnour, 435 Pa. 104, 253 A.2d 644 (1969) (opinion in support of affirmance of judgment by Bell, C. J., opinion in support of reversal of judgment by Roberts, J., in which Jones, J., joined, Cohen, J., dissented); Commonwealth v. Phelan, 427 Pa. 265, 234 A.2d 540 (1967) (majority opinion by Eagen, J., concurring opinion by Bell, C. J., dissenting opinion by Roberts, J., Cohen, J., dissented); Commonwealth v. Ahearn, 421 Pa. 311, 218 A.2d 561 (1966) (majority opinion by Bell, C. J., dissenting opinion by Roberts, J., in which Jones, J., joined, dissenting opinion by Cohen, J.). In view of our holding today, that this evidence should be allowed, our prior cases, to the extent that they suggest the contrary, are expressly overruled.
Appellant was charged with and convicted of murder of the first degree. The Legislature defined the elements of this crime as:
“All murder which shall be perpetrated by means of poison, or by lying in wait, or by any other kind of willful, deliberate and premeditated killing, or which shall be committed in the perpetration of, or attempting to perpetrate any arson, rape, robbery, burglary, or kidnapping, shall be murder in the first degree.” (Emphasis added). Penal Code, Act of June 24, 1939, P.L. 872, § 701.7
Under this section the term “willful, deliberate and premeditated” describes the mental state that must accompany the act before a nonfelony murder can be murder of the first degree. Commonwealth v. O’Searo, 466 Pa. 224, 352 A.2d 30 (filed January 1976); Commonwealth v. Fostar, 455 Pa. 216, 221, 317 A.2d 188, 190 (1974); Commonwealth v. Bricker, 458 Pa. 367, 370, 326 A.2d [217]*217279, 281 (1974); Commonwealth v. Alston, 456 Pa. 128, 129, 317 A.2d 229, 231 (1974); Commonwealth v. Mosley, 444 Pa. 134, 279 A.2d 174 (1971); Commonwealth v. Hornberger, 441 Pa. 57, 170 A.2d 195 (1970); Commonwealth v. Ewing, 439 Pa. 88, 264 A.2d 661 (1970); Commonwealth v. Jones, 355 Pa. 522, 525-526, 50 A.2d 317, 319 (1947).8
It is axiomatic that the Commonwealth must prove each element of a crime beyond a reasonable doubt. Mullaney v. Wilbur, 421 U.S. 684, 95 S.Ct. 1881, 44 L. Ed.2d 508 (1975); In Re Winship, 397 U.S. 358, 90 S.Ct. 1068, 25 L.Ed.2d 368 (1969); Commonwealth v. Graves, 461 Pa. 118, 124, 334 A.2d 661, 665 (1975); Commonwealth v. Rose, 457 Pa. 380, 389, 321 A.2d 880, 884 (1974); Commonwealth v. Bonomo, 396 Pa. 222, 151 A. 2d 880 (1959). It is equally as clear that the requisite intent of an offense is one of the elements of the crime. Mullaney v. Wilbur, supra; In Re Winship, supra; Commonwealth v. Graves, supra; Commonwealth v. Rose, supra; Commonwealth v. Bonomo, supra. Consequently, in the instant trial, it was incumbent upon the Commonwealth to prove beyond a reasonable doubt that appellant had the specific intent to kill to support the finding of murder of the first decree.
[218]*218Any analysis of the admissibility of a particular type of evidence must start with a threshold inquiry as to its relevance and probative value. Commonwealth v. Jones, 459 Pa. 62, 66, 327 A.2d 10, 13 (1974); Commonwealth v. McCusker, 448 Pa. 382, 388, 292 A.2d 286, 289 (1972). We have cited with approval the test for relevance propounded by two leading evidentiary authorities, Wigmore and McCormick. Commonwealth v. Jones, supra; Commonwealth v. Lippert, 454 Pa. 381, 384, 311 A. 2d 586, 587 (1973); Commonwealth v. McCusker, supra.
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OPINION OF THE COURT
NIX, Justice.
Today we must decide whether psychiatric evidence is admissible to be evaluated by the jury when an accused offers it to negate the element of specific intent required for a conviction of murder of the first degree thereby reducing the crime to murder of the second degree.1We [213]*213are persuaded by the vast weight of authority that psychiatric evidence should be admissible for this purpose and, therefore, we hold that the learned court below erred in excluding the proffered testimony from the jury’s consideration.2
Prior to analyzing the specific facts of this case, it is necesssary to clarify what we do not decide in today’s opinion. First, appellant has not raised the defense of [214]*214insanity and today’s decision in no way affects the vitality of the M’Naghten test as the sole standard in this Commonwealth for determining criminal responsibility where the actor alleges mental illness or defect.3 Second, for reasons that will be discussed hereinafter, we do not view the position adopted today as inferentially accepting the irresistible impulse test which we have previously expressly rejected.4
5Third, we do not here reach the question of the applicability of the principles announced herein to crimes requiring a specific intent other than murder of the first degree.
Appellant, Michael Walzack, was tried before a jury and convicted of murder of the first degree in the shooting death of one Ole Toasen. Following a penalty hearing, appellant was sentenced to life imprisonment. Post-trial motions for a new trial and in arrest of judgment were filed and denied and this direct appeal followed.6
During the trial, the defense admitted the killing and attempted to establish its position through the testimony of appellant and a Dr. Willis. When called to the stand, the defense made an offer of proof indicating that the witness did not intend to contest appellant’s sanity at the time of the incident, under the M’Naghten standard. The defense conceded that appellant was sane; that he [215]*215could tell the difference between right and wrong and that he knew the nature and quality of his act. The single stated purpose in offering the witness was to demonstrate that as a result of a surgical procedure, a lobotomy, which appellant had undergone, he did not possess sufficient mental capacity to form the specific intent required for a conviction of murder of the first degree.6
In rejecting the psychiatric evidence, the trial court relied on a number of our earlier closely divided decisions. Commonwealth v. Tomlinson, 446 Pa. 241, 284 A. 2d 687 (1971) (majority opinion by Bell, C. J., concurring opinion by Barbieri, J., dissenting opinion by Roberts, J., in which Jones and Pomeroy, JJ., joined); Commonwealth v. Weinstein, 442 Pa. 70, 274 A.2d 182 (1971) (opinion in support of affirmance of judgment by Bell, [216]*216C. J., Eagen and O’Brien, JJ., concurred in the result, opinion in support of reversal of judgment by Roberts, J., in which Jones and Pomeroy, JJ., joined); Commonwealth v. Rightnour, 435 Pa. 104, 253 A.2d 644 (1969) (opinion in support of affirmance of judgment by Bell, C. J., opinion in support of reversal of judgment by Roberts, J., in which Jones, J., joined, Cohen, J., dissented); Commonwealth v. Phelan, 427 Pa. 265, 234 A.2d 540 (1967) (majority opinion by Eagen, J., concurring opinion by Bell, C. J., dissenting opinion by Roberts, J., Cohen, J., dissented); Commonwealth v. Ahearn, 421 Pa. 311, 218 A.2d 561 (1966) (majority opinion by Bell, C. J., dissenting opinion by Roberts, J., in which Jones, J., joined, dissenting opinion by Cohen, J.). In view of our holding today, that this evidence should be allowed, our prior cases, to the extent that they suggest the contrary, are expressly overruled.
Appellant was charged with and convicted of murder of the first degree. The Legislature defined the elements of this crime as:
“All murder which shall be perpetrated by means of poison, or by lying in wait, or by any other kind of willful, deliberate and premeditated killing, or which shall be committed in the perpetration of, or attempting to perpetrate any arson, rape, robbery, burglary, or kidnapping, shall be murder in the first degree.” (Emphasis added). Penal Code, Act of June 24, 1939, P.L. 872, § 701.7
Under this section the term “willful, deliberate and premeditated” describes the mental state that must accompany the act before a nonfelony murder can be murder of the first degree. Commonwealth v. O’Searo, 466 Pa. 224, 352 A.2d 30 (filed January 1976); Commonwealth v. Fostar, 455 Pa. 216, 221, 317 A.2d 188, 190 (1974); Commonwealth v. Bricker, 458 Pa. 367, 370, 326 A.2d [217]*217279, 281 (1974); Commonwealth v. Alston, 456 Pa. 128, 129, 317 A.2d 229, 231 (1974); Commonwealth v. Mosley, 444 Pa. 134, 279 A.2d 174 (1971); Commonwealth v. Hornberger, 441 Pa. 57, 170 A.2d 195 (1970); Commonwealth v. Ewing, 439 Pa. 88, 264 A.2d 661 (1970); Commonwealth v. Jones, 355 Pa. 522, 525-526, 50 A.2d 317, 319 (1947).8
It is axiomatic that the Commonwealth must prove each element of a crime beyond a reasonable doubt. Mullaney v. Wilbur, 421 U.S. 684, 95 S.Ct. 1881, 44 L. Ed.2d 508 (1975); In Re Winship, 397 U.S. 358, 90 S.Ct. 1068, 25 L.Ed.2d 368 (1969); Commonwealth v. Graves, 461 Pa. 118, 124, 334 A.2d 661, 665 (1975); Commonwealth v. Rose, 457 Pa. 380, 389, 321 A.2d 880, 884 (1974); Commonwealth v. Bonomo, 396 Pa. 222, 151 A. 2d 880 (1959). It is equally as clear that the requisite intent of an offense is one of the elements of the crime. Mullaney v. Wilbur, supra; In Re Winship, supra; Commonwealth v. Graves, supra; Commonwealth v. Rose, supra; Commonwealth v. Bonomo, supra. Consequently, in the instant trial, it was incumbent upon the Commonwealth to prove beyond a reasonable doubt that appellant had the specific intent to kill to support the finding of murder of the first decree.
[218]*218Any analysis of the admissibility of a particular type of evidence must start with a threshold inquiry as to its relevance and probative value. Commonwealth v. Jones, 459 Pa. 62, 66, 327 A.2d 10, 13 (1974); Commonwealth v. McCusker, 448 Pa. 382, 388, 292 A.2d 286, 289 (1972). We have cited with approval the test for relevance propounded by two leading evidentiary authorities, Wigmore and McCormick. Commonwealth v. Jones, supra; Commonwealth v. Lippert, 454 Pa. 381, 384, 311 A. 2d 586, 587 (1973); Commonwealth v. McCusker, supra. Wigmore defines relevance in terms of two axioms, “None but facts having rational probative value are admissible,” and, “All facts having rational probative value are admissible, unless some specific rule forbids.” 1 Wigmore, Evidence § 9-10 at 289-95 (3rd Ed. 1940). McCormick suggests the following for determining relevance, “. . . [d]oes the evidence offered render the desired inference more probable than it would be without the evidence? . . . Relevant evidence then, is evidence that in some degree advances the inquiry, and thus has probative value, and is prima facie admissible.” McCormick, Evidence § 185 at 437-38 (2nd Ed. 1972).
In the instant case, appellant attempted to introduce expert testimony concerning his mental capacity to form the type of specific intent a conviction for murder of the first degree requires. This testimony obviously would have “significantly advanced the inquiry” as to the presence or absence of an essential element of the crime. See Commonwealth v. Hickman, 453 Pa. 427, 433-434, 309 A.2d 564, 567 (1973). Thus, the exclusion of the proffered testimony cannot be based upon a lack of relevancy. Also, there is no basis for finding the tendered testimony incompetent for other reasons. Although early decisions in this jurisdiction can be found that express doubt as to the reliability of psychiatric testimony, our more recent decisions make clear that psychiatry has a legitimate scientific basis. While recogniz[219]*219ing that psychiatry might well be less exact than some of the other medical disciplines we are nevertheless cognizant of the “tremendous advancements made in the field.” Commonwealth v. McCusker, supra at 385, 292 A.2d at 287. In Commonwealth v. McCusker, supra, after noting many of the areas in criminal law where we have accepted a psychiatrist’s opinion we observed:
“. . . [t]he reliance we have consistently placed upon the competence of psychiatric evidence belies any concern that it is not a sufficiently recognized and accepted medical science capable of offering quality expert guidance.” Id. at 392, 292 A.2d at 291.9
We have long accepted psychiatric evidence on the issue of whether an accused is competent to stand trial.10 Similarly, we have long permitted psychiatric evidence under the M’Naghten test to determine whether an accused was insane at the time of the crime.11 More recently we have allowed psychiatric evidence for the purpose of determining whether an accused acted in the heat of pas[220]*220sion when committing a homicide;12 whether an accused subjectively believed he was in imminent danger of death or serious bodily injury under his claim of self-defense ;13 whether an accused was capable of making a detailed written confession;14 and, we have long accepted psychiatric evidence at the penalty stage of trial.15
Having determined that psychiatric evidence possesses sufficient reliability for its admission for the purposes announced herein we must acertain whether there are any policy reasons that might justify ruling it incompetent. Early opinions of this Court have suggested that acceptance of the doctrine of diminished capacity is tantamount to acceptance of the irresistible impulse test for insanity.16 We do not agree. The doctrines of [221]*221diminished capacity and irresistible impulse involve entirely distinct considerations. Irresistible impulse is a test for insanity which is broader than the M’Naghten test. Under the irresistible impulse test a person may avoid criminal responsibility even though he is capable of distinguishing between right and wrong, and is fully aware of the nature and quality of his act provided he establishes that he was unable to refrain from acting. An accused offering evidence under the theory of diminished capacity concedes general criminal liability. The thrust of this doctrine is to challenge the capacity of the actor to possess a particular state of mind required by the legislature for the commission of a certain degree of the crime charged.
In adopting the position we announce today, we are buttressed by the fact that many jurisdictions in the country accept this view.17 Of these jurisdictions, a number of them embrace the M’Naghten rule as we do.18
In recognizing the validity of this doctrine, the Supreme Court of Colorado reasoned:
“A defendant in a first degree murder case has the right, without reference to a plea of insanity, to establish mental deficiency as bearing upon his capacity to [222]*222form the specific intent essential to first degree murder.” Beeksted v. People, 133 Colo. 72, 292 P.2d 189 (1956).
See, also, Battalino v. People, 118 Colo. 587, 199 P.2d 897 (1948); Leick v. People, 131 Colo. 353, 281 P.2d 806 (1955). In a more expansive explanation of the rationale supporting this view, the Iowa Supreme Court stated:
We believe that failure to recognize there can be an unsoundness of mind of such a character as to negative a specific intent to commit a particular crime, is to ignore the great advancements which have been made in the field of psychiatry. The results which have been achieved confirm its growing reliability. We do not consider this position contradictory to our adherence to the right and wrong test of insanity. We do not pretend there are no mental disorders except those which qualify under this test, but rather limit the defense of insanity to the types of mental illness in which the defendant cannot comprehend the nature or consequences of his act. Weihofen in his text Mental Disorder as a Criminal Defense states that if we recognize the basic principle that a person should not be punished for a crime if he did not entertain the requisite state of mind, “there is no logical escape from the proposition that a person cannot be held guilty of a deliberate and premeditated killing when he did not deliberate and premeditate, and indeed was incapable of deliberating and premeditating. If, however, he was able to understand the nature of the act he was committing and if he intended to do that act, he should be held guilty of murder in the second degree or manslaughter. There is no logic in the ‘all or nothing’ assumption underlying so many court opinions on the subject — that a person is either ‘sane’ and wholly responsible for all his acts, or ‘insane’ and wholly [223]*223irresponsible.” 19 State v. Gramenz, 256 Iowa 134, 126 N.W.2d 285 (1964).
Once it is determined that the proffered evidence was both relevant and competent, due process requires its admission. Article I, Section 9 of the Pennsylvania Constitution sets forth the rights of an accused in criminal prosecutions.
“Even the most myopic interpretation of this clause would necessarily concede the right to offer relevant evidence to challenge a material issue of fact.” Commonwealth v. Graves, supra, at 334 A.2d at 665, n. 7.20
It is inconsistent with fundamental principles of American jurisprudence to preclude an accused from offering relevant and competent evidence to dispute the charge against him. This, of course, includes any of the elements that comprise that charge.
Judgment of sentence reversed and a new trial awarded.
[224]*224EAGEN, J., filed a dissenting opinion in which O’BRIEN, J., joins.