In each of the four cases before us, the defendant was convicted of conspiracy to commit first-degree murder and sentenced to life imprisonment, pursuant to MCL 750.316; MSA 28.548. We have consolidated these cases on appeal to decide the limited issue whether a person sentenced to life imprisonment for conspiracy to commit first-degree murder is eligible for parole consideration under MCL 791.234(4); MSA 28.2304(4) and the proper retroactive effect of such a decision. We conclude that the existing statutory scheme governing conspiracy and its punishment does not preclude parole consideration for defendants convicted of conspiracy to commit first-degree murder. Our decision has retroactive application.
i
Defendants Tipsword and Dudgeon were convicted by a jury in 1975 of conspiracy to commit first-degree murder and sentenced to life imprisonment. The defendants and two others conspired, for pay, to kill an Oak Park resident because of a "family problem.” The planned murder was foiled when, on the night in question, the mother of the intended victim refused to answer a suspicious late night knock on the door of her residence and instead called the police. Defendants fled the scene and were apprehended shortly thereafter. In a consolidated appeal, the Court of Appeals affirmed defendants’ convictions and, upon remand ordered by this Court for the purpose of deciding the *494present issue, held that defendants were eligible for parole consideration.
Defendant Jones was convicted of two counts of conspiracy to commit first-degree murder and was sentenced to life imprisonment for conspiring to kill two business partners. The plan was thwarted when the assassin selected by the defendant turned out to be a state trooper. The Court of Appeals affirmed defendant’s convictions and subsequently held upon remand that defendant’s sentence was nonparolable. 167 Mich App 424; 423 NW2d 590 (1988).
Defendant Jahner was convicted by a jury of conspiracy to commit first-degree murder and assault with intent to murder. She was sentenced to life imprisonment for the conspiracy conviction and ten to twenty years imprisonment for the assault. Defendant conspired with another person to kill her stepmother. The victim was injured in the murder attempt, but recovered and testified at trial. Defendant’s conviction of conspiracy to commit first-degree murder was ultimately held by order of the Court of Appeals to be a nonparolable offense.
Upon application for leave to appeal in this Court, these four cases were consolidated for consideration of the parole eligibility issue.
ii
The present question involves the interplay of three statutes. The conspiracy statute was enacted as 1966 PA 296. It reads, in relevant part:
Any person who conspires together with 1 or more persons to commit an offense prohibited by law, or to commit a legal act in an illegal manner is guilty of the crime of conspiracy punishable as provided herein:
*495(a) Except as provided in paragraphs (b), (c) and (d) if commission of the offense prohibited by law is punishable by imprisonment for 1 year or more, the person convicted under this section shall be punished by a penalty equal to that which could be imposed if he had been convicted of committing the crime he conspired to commit and in the discretion of the court an additional penalty of a fine of $10,000.00 may be imposed. [MCL 750.157a; MSA 28.354(1).]
Thus, the penalty for conspiracy is vicarious and depends upon the target offense penalty where the target offense is punishable by imprisonment for one year or more. The defendants in the instant cases were charged with and convicted of conspiracy to commit first-degree murder. MCL 750.316; MSA 28.548, the first-degree murder statute, reads:
Murder which is perpetrated by means of poison, lying in wait, or other wilful, deliberate, and premeditated killing, or which is committed in the perpetration, or attempt to perpetrate arson, criminal sexual conduct in the first or third degree, robbery, breaking and entering of a dwelling, larceny of any kind, extortion, or kidnapping, is murder of the first degree, and shall be punished by imprisonment for life.
Finally, the so-called "lifer law” provides that those convicted of the substantive crime of first-degree murder are not eligible for parole consideration:
A prisoner under sentence for life or for a term of years, other than prisoners sentenced for life for murder in the first degree and prisoners sentenced for life or for a minimum term of imprisonment for a major controlled substance offense, who has served 10 calendar years of the sentence is subject to the jurisdiction of the parole board and may be *496released on parole by the parole board .... [MCL 791.234(4); MSA 28.2304(4).1 Emphasis added.]
Although a statute may appear to be unambiguous on its face, "it can be rendered ambiguous by its interaction with and its relation to other statutes.” 2A Sands, Sutherland Statutory Construction, § 46.04, pp 86-87. Such is the case here. The question of parole eligibility for defendants convicted of conspiracy to commit first-degree murder cannot be answered by reference to the conspiracy statute alone, since that statute, by its terms, does not address the parole issue. Similarly, although the first-degree murder statute provides for mandatory life imprisonment, it too is silent with respect to parole implications. What makes first-degree murder a nonparolable offense is the "lifer law,” which specifically excludes persons convicted of first-degree murder from the jurisdiction of the Parole Board after serving ten calendar years of the sentence. However, the "lifer law” does not similarly exclude defendants convicted of the crime of conspiracy to commit first-degree murder from the scope of its coverage. This is the heart of the present controversy over which the Court of Appeals panels have split evenly in the present cases. Should the express exclusion of first-degree murder from parole eligibility be extended by implication to the crime of conspiracy to commit *497first-degree murder?2 We are constrained to respond in the negative.
hi
In each of the cases before us, the crime which was the object of the conspiracy did not come to fruition. None of the intended victims was killed. That the intended murders in these cases never occurred does not detract from the seriousness of the offenses, see People v Fernandez, 427 Mich 321, 336; 398 NW2d 311 (1986); however, it does *498underscore an important distinction between the crime of conspiracy to commit first-degree murder and the crime of first-degree murder itself:
It is a settled principle of black-letter law that conspiracy is a crime that is separate and distinct from the substantive crime that is its object. LaFave & Scott, Criminal Law, § 62, p 494; People v Tinskey, 394 Mich 108; 228 NW2d 782 (1975); People v Chambers, 279 Mich 73; 271 NW 556 (1937). The guilt or innocence of a conspirator does not depend upon the accomplishment of the goals of the conspiracy. [People v Carter, 415 Mich 558, 569; 330 NW2d 314 (1982).]
While defendants in these cases were found guilty of an extremely heinous offense, it cannot be said that they were convicted of first-degree murder. Accordingly, the parole prohibition in the "lifer law” which expressly applies to first-degree murder does not apply to the separate and distinct crime of conspiracy to commit that offense. Criminal statutes are to be strictly construed:
It is a fundamental rule of construction of criminal statutes that they cannot be extended to cases not included within the clear and obvious import of their language. And if there is doubt as to whether the act charged is embraced in the prohibition, that doubt is to be resolved in favor of the defendant. In other words, nothing is to be added by intendment. [People v Ellis, 204 Mich 157, 161; 169 NW 930 (1918).]
This rule is most commonly applied in defining those actions that come within the scope of a statutory prohibition. As explained in People v Willie Johnson, 75 Mich App 221, 225; 255 NW2d 207 (1977), aff'd 406 Mich 320; 279 NW2d 534 (1979):
*499The principle requires that doubtful conduct be found not criminal. In large part, the principle in those cases is based on the idea of notice, but this rule of strict construction of penal or criminal statutes also reflects the idea that it is the job of the Legislature to define criminal offenses and punishment. Restraint by the courts in interpreting criminal statutes works to avoid judicial infringement of that legislative function.
Strict construction also serves to guard against the dangers of arbitrary and discriminatory application of otherwise vague legislative pronouncements. People v Howell, 396 Mich 16, 20, n 4; 238 NW2d 148 (1976).
Similar considerations have given rise to the "rule of lenity.” In People v Bergevin, 406 Mich 307, 312; 279 NW2d 528 (1979), this Court quoted from Bell v United States, 349 US 81, 83; 75 S Ct 620; 99 L Ed 905 (1955):
"When Congress leaves to the Judiciary the task of imputing to Congress an undeclared will, the ambiguity should be resolved in favor of lenity. And this is not out of any sentimental consideration, or for want of sympathy with the purpose of Congress in proscribing evil or anti-social conduct. It may fairly be said to be a presupposition of our law to resolve doubts in the enforcement of a penal code against the imposition of a harsher punishment.”
See also People v Gilbert, 414 Mich 191, 211; 324 NW2d 834 (1982); People v Dempster, 396 Mich 700, 715; 242 NW2d 381 (1976); People v Willie Johnson, supra, pp 224-225.
The rule of lenity operates in favor of an accused, mitigating punishment when punishment is unclear. Thus, in the instant cases, where the *500defendants are convicted of an offense for which the penalty provisions are ambiguous, particularly where the potential penalty is the harshest possible under state law, we are hesitant to add by inference another exception to the "lifer law.”3 The practical effect would be to eliminate Parole Board discretion on this issue. Under the circumstances, we are unwilling to set into play these ramifications without further direction from the Legislature. The Legislature, not this Court, has the exclusive power to designate the grade and prescribe the punishment of offenses. Attorney General v Recorder’s Court Judge, 341 Mich 461, 474-475; 67 NW2d 708 (1954); People v Causley, 299 Mich 340, 348; 300 NW 111 (1941). Furthermore, it is the duty of this Court to interpret a statute as we find it:
The wisdom of the provision in question in the form in which it was enacted is a matter of legislative responsibility with which courts may not interfere. Michigan & Vicinity Foundry Workers *501Union v Enterprise Foundry Co, 321 Mich 265 [32 NW2d 515 (1948)]. As tersely stated by Chief Justice Butzel in Roosevelt Oil Co v Secretary of State, 339 Mich 679, 694 [64 NW2d 582 (1954)], "It is the function of the court to fairly interpret a statute as it then exists; it is not the function of the court to legislate.” [Melia v Employment Security Comm, 346 Mich 544, 561-562; 78 NW2d 273 (1956).]
Resolution of this issue in favor of parole is reinforced by another significant consideration.4 Since enactment of the conspiracy statute in 1976, the "lifer law” has been amended twice, in 1978 and 1982. Until 1978, only first-degree murderers were expressly excepted from the "lifer law.” In 1978, in the course of a comprehensive revision of the controlled substances statute, persons convicted of a major controlled substance offense, as well as those convicted of conspiracy to commit such offenses, were expressly excepted from the "lifer law” and thus were deprived of its benefits. See MCL 791.233b(l); MSA 28.2303(2X1). The "lifer law” has not been similarly amended to expressly except from parole eligibility those convicted of conspiracy to commit first-degree murder.
The prosecution in the instant cases places undue emphasis on the term "penalty” as it is used in the conspiracy statute. The Court of Appeals in Jones (On Remand), supra, p 427, posited that
*502[w]hile one may argue that parole eligibility is not appurtenant to a sentence imposed for a particular conviction, the same cannot be said for the penalty imposed. The lack of parole eligibility is undoubtedly a "penalty” imposed upon a person sentenced to life imprisonment for first-degree murder. Hence, the conspiracy statute mandates a like penalty for a person sentenced to life imprisonment for a conspiracy to commit first-degree murder.
This approach overlooks the independent nature of the conspiracy statute and the "lifer law” vis-ávis one another. While the conspiracy statute and the "lifer law” both address in general terms the punishment of criminal activity and therefore should be read in pari materia, the two statutes address separate and distinct considerations. The conspiracy statute is directed to the trial court and requires that it impose a particular "penalty” for the offense. However, the statutory command is discharged at the time of sentencing. By contrast, the "lifer law” is not directed at the sentencing court, but rather governs the power and authority of the Parole Board to grant parole under certain circumstances. Given the autonomy granted to the Parole Board and the separate function which it serves, we do not believe that the term "penalty” as it is used in the conspiracy statute encompasses the parole considerations set forth in the "lifer law.”
Our prior treatment of parole as an element of the sentencing process supports this conclusion. In Guilty Plea Cases, 395 Mich 96, 118; 235 NW2d 132 (1975), this Court ruled that the trial judge need not inform the defendant of all sentence consequences — only the maximum sentence for the crime to which he was pleading guilty. In subsequent cases, the Michigan courts have held that a *503defendant’s eligibility for parole, or good time, or any other factor that affects his actual release date, is not a sentence consequence of which a defendant need be advised when pleading guilty. See, e.g., People v Johnson, 413 Mich 487; 320 NW2d 876 (1982); People v Price, 124 Mich App 717, 721-722; 335 NW2d 134 (1983); People v King, 111 Mich App 363; 314 NW2d 622 (1981). Thus, it would be inconsistent in the present context to find that the term "penalty” as it is used in the conspiracy statute extends to parole considerations.
The prosecution also points to the Legislature’s presumed awareness of existing law when it enacts new legislation, People v Timothy Smith, 423 Mich 427, 441-442; 378 NW2d 384 (1985), as another basis for precluding parole eligibility. As the Jones Court theorized in its opinion on remand, the Legislature is presumed to have known that first-degree murder was nonparolable at the time it proclaimed in the conspiracy statute that one convicted of conspiracy is to receive a penalty equal to that which could be imposed for the substantive offense. Jones, supra, pp 426-427. See also People v Fernandez (On Remand), 164 Mich App 485, 489; 417 NW2d 540 (1987) (Gnus, J., dissenting).
However, this presumption is contradicted by the fact that until relatively recently, there was a legitimate question — and difference of judicial opinion — on the more fundamental issue whether a conspiracy to commit first-degree murder conviction even required a mandatory life sentence pursuant to the language of the first-degree murder statute. See People v Fernandez, supra.
Moreover, the rules of statutory construction do not sustain the presumption of legislative knowledge under these particular circumstances:
*504The rule, in pari materia, does not permit the use of a previous statute to control by way of former policy the plain language of a subsequent statute; much less to add a condition or restriction thereto found in the earlier statute and left out of the later one. The contention made, if allowed, would go beyond the construction of the statute, and engraft upon its provisions a restriction which the legislature might have added but left out. [Voorhies v Recorder’s Court Judge, 220 Mich 155, 157-158; 189 NW 1006 (1922). See also People ex rel Pellow v Byrne, 272 Mich 284, 288; 261 NW 326 (1935); Reichert v Peoples State Bank, 265 Mich 668, 672; 252 NW 484 (1934).]
We cannot assume that the Legislature misrepresented its intent when it limited exceptions to the "lifer law” to those offenses listed in the exceptions clause of MCL 791.234(4); MSA 28.2304(4).
We therefore conclude that a person sentenced to life imprisonment for conspiracy to commit first-degree murder is eligible for parole consideration, pursuant to MCL 791.234(4); MSA 28.2304(4).
This decision constitutes a clarification of existing law and, as such, is entitled to retroactive application. People v Kamin, 405 Mich 482; 275 NW2d 777 (1979).
IV
Accordingly, in People v Tipsword and People v Dudgeon, we affirm the decision of the Court of Appeals.
In People v Jones and People v Jahner, we reverse the decisions of the Court of Appeals.
Riley, C.J., and Levin, Brickley, Cavanagh, and Archer, JJ., concurred with Griffin, J.A fourth statute which requires mention is MCL 791.233(3); MSA 28.2303(3), as amended by 1978 PA 81. That statute, otherwise known as Proposal b, prohibits parole in certain cases until the minimum sentence is actually served. Proposal b was interpreted, until 1984, to preclude parole consideration for persons serving life sentences because the minimum sentence of a life sentence is life. However, this Court subsequently held that Proposal b applies only to indeterminate sentences, not fixed or life sentences. People v Johnson, 421 Mich 494, 498; 364 NW2d 654 (1984). Thus, as this Court stated in People v Fernandez, 427 Mich 321, 333; 398 NW2d 311 (1986), "there is no apparent restriction arising from Proposal b on application of the 'lifer law’ to a life sentence imposed for conspiracy to commit first-degree murder.”
That there might be a problem of statutory interpretation regarding parole eligibility first became apparent to this Court in People v Fernandez, n 1 supra, pp 330-331, 333, where we held that a mandatory life sentence is required for a conviction of conspiracy to commit first-degree murder. We remanded that case to the Court of Appeals for consideration of the parole eligibility issue, explaining:
While the possibility of parole was an underlying concern in the Court of Appeals and in the briefs submitted to this Court, the Court below and the parties’ briefs assumed that once a life sentence was imposed by the conjunction of §§ 157a and 316, there was no possibility of parole. At oral argument, the idea first arose that such a life sentence could qualify under MCL 791.234(4); MSA 28.2304(4), the "lifer law,” for parole consideration after ten years.
While MCL 791.234(4); MSA 28.2304(4) specifically excludes those sentenced for murder in the first-degree from the provisions of the "lifer law,” there is no such exclusion for those sentenced to life for conspiracy to commit first-degree murder under MCL 750.157a; MSA 28.354(1). Thus, as the prosecutor observed at oral argument, there is no apparent reason in the "lifer law” itself that would preclude the possibility of parole in Mr. Fernandez’ case.
Because this issue was not briefed by the parties and there has been no opportunity for amici curiae like the Parole Board to file briefs, we remand this case to the Court of Appeals for briefing and decision on this issue.
On remand, the Court of Appeals concluded that there was parole eligibility. 164 Mich App 485; 417 NW2d 540 (1987). No further appeal was pursued in Fernandez subsequent to the Court of Appeals decision on remand.
Another pertinent rule of statutory construction provides that "inclusion by specific mention excludes what is not mentioned.” Van Sweden v Van Sweden, 250 Mich 238, 241; 230 NW 191 (1930). Statutory exceptions are to be accorded limited, rather than expansive construction:
[I]t is not the province of this court to make an exception where the legislature has made none. The rule of construction is that the exception, if any, shall appear in the act. [Arends v Grand Rapids R Co, 172 Mich 448, 450-451; 138 NW 195 (1912). See also Northville Coach Line, Inc v Detroit, 379 Mich 317, 329; 150 NW2d 772 (1967) (plurality opinion); Rzepka v Farms Estates, Inc, 83 Mich App 702, 707; 269 NW2d 270 (1978).]
A related, consistent principle of statutory construction is that the express mention in a statute of one thing implies the exclusion of other similar things (expressio unius est exclusio alterius), Stowers v Wolodzko, 386 Mich 119, 133; 191 NW2d 355 (1971); Sebewaing Ind v Village of Sebewaing, 337 Mich 530, 545-546; 60 NW2d 444 (1953); Ellis v Wakefield Twp School Dist, 79 Mich App 347, 350; 261 NW2d 320 (1977).
Unfortunately, despite our invitation in Fernandez, supra, p 333, to the Parole Board to file a brief on this issue as amicus curiae, little information has been generated regarding the actual practice of the Parole Board and its treatment of defendants sentenced to life for a conspiracy to commit first-degree murder. There is no written Parole Board policy. Thus, we cannot benefit one way or the other from the interpretative aid that the " 'construction placed upon statutory provisions by any particular department of government for a long period of time . . . should be given considerable weight.’ ” Melia v Employment Security Comm, supra, p 565. Defendant Jahner’s record suggests that the Parole Board has been routinely reviewing her case since 1984 as a "lifer law” case.