(concurring). In Commonwealth v. Joyce, 382 Mass. 222, 231 n.8 (1981), we left open the question whether, in a case like this, a defendant could introduce in evidence under G. L. c. 233, § 21, records of convictions of prostitution, or other sex-related crimes, to impeach a rape complainant’s credibility. Today, the plurality opinion suggests “that the rape-shield provisions . . . exclude this kind of evidence even when it involves the complainant’s convictions submitted to impeach the complainant’s credibility generally. Thus, despite G. L. c. 233, § 21, the trial judge generally does not have discretion to admit such convictions. ... A complainant’s convictions involving sexual conduct could be admissible if they are clearly relevant to a motive to lie or to bias ... or fall within the two statutory exceptions of the rape-shield statute.”1 Ante at 625-626.
I cannot agree that a trial judge lacks the discretion to admit past sex-related convictions to impeach a complainant’s credibility. I would hold that the rape-shield statute does not per se preclude a judge from exercising discretion to permit the defendant to offer convictions of past sex-related crimes against a complainant for impeachment purposes.
The plurality opinion identifies a potential conflict between G. L. c. 233, § 21, the statute that permits impeachment by prior conviction, and G. L. c. 233, § 21B, the rape-shield statute. Pursuant to § 21, a prior conviction is admissible to impeach the credibility of a witness when the prior conviction meets certain requirements. Section 21B provides that “[e]vi-*630dence of specific instances of a victim’s sexual conduct . . . shall not be admissible except evidence of the victim’s sexual conduct with the defendant or evidence of recent conduct of the victim alleged to be the cause of any physical feature, characteristic, or condition of the victim.” The plurality reads § 21B as creating an exception to § 21 to prevent the use of sex-related convictions to impeach a rape complainant except when the convictions are relevant to a motive to lie or bias.
The plurality justifies its conclusion by noting that the purpose of the rape-shield statute is to protect rape victims and that, because the rape-shield statute was enacted after the impeachment by prior conviction statute, ante at 624 n.ll, its provisions should control. Certainly I agree that protecting rape victims from the unfair admission of their past sexual conduct is an important legislative goal advanced by the rape-shield statute.
Where two statutes conflict, however, as they appear to do here, our first task is to attempt to harmonize the respective provisions of both. We do not favor the implied repeal of statutory provisions. LaBranche v. A.J. Lane & Co., 404 Mass. 725, 728-729 (1989), citing Dedham Water Co. v. Dedham, 395 Mass. 510, 518 (1985). Cohen v. Price, 273 Mass. 303, 308 (1930), quoting Brown v. Lowell, 8 Met. 172, 174-175 (1844). We only prefer the later enacted statute after we have determined that the two statutes are irreconcilable. In my view, the statutes can coexist without repealing a portion of the impeachment by prior conviction statute or abandoning the policy of protecting rape victims from unfair examination regarding past sexual conduct.
When enacting § 21B, the Legislature was presumably aware of the provisions of § 21. The provisions appear within the same chapter of the General Laws; only one section separates §21 and § 21B. As the plurality states, the Legislature considered but did not adopt language that would have expressly stated that the use of prior sex-related convictions to impeach credibility was not limited by the rape-shield statute. The plurality suggests that this legislative inaction shows that “the Legislature did not want such convictions to be admissible for the impeachment of a rape complainant’s credibility.” Ante at 625. Ascertaining meaning from the Legislature’s decision not to enact statutory language, however, is an uncertain endeavor. It must be acknowledged that the Legislature has not altered the words of the prior statute. It has not repealed them or altered *631them in any form. The principal way the courts ascertain the intent of the Legislature is through the language the Legislature chooses. Here we have language in § 21 which presumably the Legislature intends us to implement. We should be guided by the familiar principle of statutory interpretation that “[a] statute is not to be deemed to repeal or supersede a prior statute in whole or in part in the absence of express words to that effect or of clear implication.” Commonwealth v. Hayes, 372 Mass. 505, 512 (1977), quoting Colt v. Fradkin, 361 Mass. 447, 449-450 (1972).
The Legislature has not expressly stated or clearly implied that the rape-shield statute prevents the defendant from introducing sex-related convictions to impeach the credibility of a rape complainant. Therefore, the more plausible course is to construe the legislative will as intending that the policies embraced in both statutes be enforced. It is not the function of this court to develop policy. Both statutes exist and should be implemented, if at all possible. Boston Hous. Auth. v. Labor Relations Comm’n, 398 Mass. 715, 718 (1986), citing Hadley v. Amherst, 372 Mass. 46, 50-51 (1977). Everett v. Revere, 344 Mass. 585, 589 (1962). The Legislature is the body for enacting social policy change. In the absence of a clear expression of legislative intent to limit § 21, I would conclude that sex-related convictions are admissible to impeach the credibility of a rape complainant.
Perceived in this manner, § 21B indicates a general policy to exclude evidence of the sexual conduct of a victim. Section 21 is an exception to that general policy which applies in a narrow class of cases, i.e, when the witness has actually been convicted of offenses within a certain time period, subject to the judge’s discretion to exclude the conviction if the judge determines that its prejudicial effect outweighs its probative value. See Commonwealth v. Drumgold, 423 Mass. 230, 249 (1996). Section 21 is very narrow compared to the breadth of § 21B which relates to all other evidence of sexual activity.
It is not illogical for the Legislature to carve out this exception for convictions. Convictions bear indicia of reliability that distinguish them from other types of evidence that are excluded by § 21B, further indicating that the Legislature intended both these statutes to apply.
I would conclude that a prior conviction is admissible for the limited purpose of attacking the credibility of the witness. See *632G. L. c. 233, § 21 (“[t]he conviction of a witness of a crime may be shown to affect his credibility”). It is not admissible for any other purpose. Indeed, the jury must be instructed that its only purpose is to impeach the credibility of the complainant. This interpretation of the two sections permits us to give effect to each of the pronouncements of the Legislature.
Despite my belief that the rape-shield statute does not prohibit the admissibility of sex-related convictions for impeachment purposes, the important policy considerations underlying due process and the right to a fair trial require the trial judge to exercise discretion in deciding to permit the introduction of convictions for impeachment. Because of the distinct danger that a jury will consider sex-related convictions to bear on the propensity of the complainant to engage in sexual conduct, a trial judge should exercise caution before admitting these convictions. See Commonwealth v. Fano, 400 Mass. 296, 303 (1987) (admission of prior conviction substantially similar to crime being tried presents risk that jury may be diverted from question of defendant’s guilt to question of defendant’s bad character). The judge should consider whether there is other available evidence to impeach the complainant’s credibility including convictions that are not sexual in nature. Furthermore, a judge should instruct the jury as to the limited evidentiary purpose of the convictions.
In this case the prostitution-related convictions of the complainant met the admissibility criteria of § 21. The judge had discretionary authority to admit the convictions and he chose to exclude them. He exercised his discretion fairly. He decided to exclude both the complainant’s prostitution convictions and a prior indecent assault and battery conviction the Commonwealth sought to introduce against the defendant. The judge did not abuse his discretion in excluding the prostitution convictions. Thus, I concur that the defendant’s conviction of aggravated rape should be affirmed.
While this concurrence is based on other grounds, I note that there is some ambiguity in the plurality opinion. The quoted language suggests that prior convictions are admissible to show motive or bias. It is my opinion that prior convictions are admissible for a single purpose: to impeach credibility. See G. L. c. 233, § 21. Apart from the narrow exception created by § 21, the prior convictions would be inadmissible as hearsay and as non-expert opinion. I assume that the plurality means that the rape-shield statute does not render inadmissible evidence of prior sexual activity of the complainant apart from convictions when offered for the purpose of showing bias or motive.