CHIN, J.

Defendants sentenced to prison for criminal conduct are entitled to credit against their terms for all actual days of presentence and postsentence custody (Pen. Code, §§ 2900, subd. (c), 2900.5, subds. (a), (b)) and while in prison custody, can earn postsentence good behavior/worktime credits (§ 2931) or prison worktime credits (§ 2933) to shorten the period of incarceration. Defendants detained in a county jail, or other equivalent specified facility, "prior to the imposition of sentence," may also be eligible for presentence good behavior/worktime credits (collectively referred to as conduct credits) of up to two days for every four days of actual custody. (§ 4019, subds. (a)(4), (b), (c), (e), (f).) Section 2933.1, subdivision (c), adopted in 1994, limits the authorized award of presentence conduct credits to a maximum of 15 percent of a defendant's actual period of presentence confinement for specified felons, including murderers. In this case, a jury convicted defendant for a murder that was committed on May 22, 1998. We granted review to determine whether the 15 percent limitation on presentence conduct credits applies to convicted murderers, such as defendant, who were sentenced under the 1978 version of section 190, which designates the punishment for murder. As explained below, we conclude that section 2933.1 applies to limit defendant's award of presentence conduct credits.

factual background

Defendant appealed and claimed, among other things, that the trial court miscalculated his presentence conduct credits under section 2933.1. Agreeing with defendant that the trial court erred in limiting those credits, the Court of Appeal awarded defendant full presentence conduct credits, as authorized under section 4019. The court modified the judgment by increasing the presentence conduct credits from 50 days to 168 days, but otherwise affirmed the conviction.

Defendant sought review here on an instructional issue not before us. The Attorney General filed a letter, which we deemed to be an answer, contesting the modification of sentence. We granted review solely on the credits issue.

discussion

As in the Court of Appeal, defendant asserts that his murder sentence was based on the 1978 version of section 190, which had been adopted by the electorate by the passage of the Briggs Initiative. He argues that, because section 2933.1 was enacted by the Legislature in 1994 without voter approval, the limitation of presentence conduct credits against that sentence was an invalid modification of the Briggs Initiative. For the reasons stated below, we disagree.

On November 7, 1978, the voters amended section 190 by the passage of the Briggs Initiative. The amendment increased the punishment for first degree murder from an indeterminate term of life imprisonment to a term of 25 years to life, and for second degree murder from a term of five, six, or seven years to 15 years to life in state prison. (Prop. 7, as approved by voters, Gen. Elec. (Nov. 7, 1978); see Note, Deering's Ann. Pen. Code (1985 ed.) foll. § 190, p. 82; People v. Bright (1996) 12 Cal.4th 652, 662-663, fn. 7.) The purpose of the Briggs Initiative was to substantially increase the punishment for persons convicted of first and second degree murder. ( In re Jeanice D. (1980) 28 Cal.3d 210, 219.) Former section 190, as amended by the Briggs Initiative, provided for credits as follows: "The provisions of Article 2.5 (commencing with Section 2930) of Chapter 7 of Title 1 of Part 3 of the Penal Code shall apply to reduce any minimum term of 25 or 15 years in state prison imposed pursuant to this section, but such person shall not otherwise be released on parole prior to such time." (Prop. 7, as approved by voters, Gen. Elec. (Nov. 7, 1978), reprinted at Deering's Ann. Pen. Code, supra, § 190, p. 82 (former § 190.3).)

At the time the Briggs Initiative was approved, article 2.5 contained only provisions relating to prison conduct credits: sections 2930 (notice to prisoners about availability of credits), 2931 (good behavior and participation credits), and 2932 (forfeiture of such credits). (Stats. 1976, ch. 1139, § 276, pp. 5146-5149; In re Oluwa (1989) 207 Cal.App.3d 439, 442.) The Legislature had enacted article 2.5 as part of the Determinate Sentencing Act of 1976, to provide incentives for prison inmates to refrain from criminal conduct and to encourage participation in rehabilitative activities by allowing inmates to reduce their sentences for good behavior and participation in prison activities. ( People v. Austin (1981) 30 Cal.3d 155, 163.)

In 1988 and 1994, the voters again approved legislative amendments to section 190 by the passage of Propositions 67 and 179, respectively. The amendments increased the penalties for certain designated murders not applicable here, consistent with the purpose of the Briggs Initiative to increase the punishment for persons convicted of murder. (Stats. 1987, ch. 1006, § 1, pp. 3367-3368, approved by voters as Prop. 67, eff. June 8, 1988; Ballot Pamp., Primary Elec. (June 7, 1988) analysis and text of Prop. 67, pp. 8-9; and see Legis. Counsel's Dig., Sen. Bill No. 402, 4 Stats. 1987, Summary Dig., p. 335; Stats. 1993, ch. 609, § 3, p. 3266, approved by voters as Prop. 179, eff. June 8, 1994; Ballot Pamp., Primary Elec. (June 7, 1994) analysis, text, and argument in favor of Prop. 179, pp. 22-23, 29; and see Legis. Counsel's Dig., Sen. Bill. No. 310, 5 Stats. 1993, Summary Dig., pp. 236-237; see Notes, Deering's Ann. Pen. Code (2001 supp.) foll. § 190, pp. 38-39.)

At the time of the murder in this case (May 1998), the credits provision in subdivision (a) of former section 190, as amended effective 1994, read: "Except as provided in subdivision (b), Article 2.5 (commencing with Section 2930) of Chapter 7 of Title 1 of Part 3 shall apply to reduce any minimum term of 15, 20, or 25 years in the state prison imposed pursuant to this section, but the person shall not otherwise be released on parole prior to that time." (Stats. 1993, ch. 609, § 3, p. 3266.)

In 1994, the Legislature added section 2933.1 to article 2.5 as an urgency measure. (Stats. 1994, ch. 713, § 1, p. 3448.) For specified felons, section 2933.1 limits presentence conduct credits authorized under section 4019. ( People v. Buckhalter (2001) 26 Cal.4th 20, 31-32; People v. Aguirre, supra, 56 Cal.App.4th at pp. 1138-1141.) Section 2933.1 became effective on September 21, 1994 ( People v. Camba (1996) 50 Cal.App.4th 857, 867), after the passage of Proposition 179, and states, in relevant part: "(a) Notwithstanding any other law, any person who is convicted of a felony offense listed in Section 667.5 shall accrue no more than 15 percent of worktime credit, as defined in Section 2933. [¶] . . . [¶] (c) Notwithstanding Section 4019 or any other provision of law, the maximum credit that may be earned against a period of confinement in, or commitment to, a county jail, . . . following arrest and prior to placement in the custody of the Director of Corrections, shall not exceed 15 percent of the actual period of confinement for any person specified in subdivision (a)."

Murder is one of the qualifying felony offenses specified in section 667.5, subdivision (c)(1).

Relying on In re Oluwa, supra, 207 Cal.App.3d at page 445, defendant argues that, at the time of his offense, former section 190 incorporated by specific reference the code sections contained in article 2.5 at the time of the Briggs Initiative. Because former section 190 expressly authorized article 2.5 credits to reduce the minimum term imposed and section 2933.1 later limited the availability of credits without voter approval, defendant claims that section 2933.1 is inapplicable to his sentence. He argues that, instead, he is entitled to presentence conduct credits under the more favorable section 4019 formula. On the other hand, the Attorney General argues that former section 190's reference to article 2.5 in the 1978 Briggs Initiative was "merely a general reference to an entire system of laws regarding credits" and that any subsequent credits modifications by the Legislature were to be included in section 190's general reference to the credits scheme. We agree with defendant's characterization that the reference to article 2.5 was a specific reference rather than a general one, as asserted by the Attorney General. Nevertheless, although we reject the Attorney General's underlying analysis, we agree with him that the trial court's application of the section 2933.1 credits limitation against his sentence was not an invalid modification of the Briggs Initiative.

A statute enacted by voter initiative may be changed only with the approval of the electorate unless the initiative measure itself permits amendment or repeal without voter approval. (Cal. Const., art. II, § 10, subd. (c).) The Briggs Initiative did not authorize the Legislature to amend its provisions without voter approval. ( In re Oluwa, supra, 207 Cal.App.3d at pp. 445-446.) "'It is a well established principle of statutory law that, where a statute adopts by specific reference the provisions of another statute, regulation, or ordinance, such provisions are incorporated in the form in which they exist at the time of the reference and not as subsequently modified. . . . [Citations.] [¶] . . . [¶] . . . [T]here is a cognate rule, recognized as applicable to many cases, to the effect that where the reference is general instead of specific, such as a reference to a system or body of laws or to the general law relating to the subject in hand, the referring statute takes the law or laws referred to not only in their contemporary form, but also as they may be changed from time to time, and . . . as they may be subjected to elimination altogether by repeal. [Citations.]'" ( Palermo v. Stockton Theatres, Inc. (1948) 32 Cal.2d 53, 58-59.) An amendment is a legislative act designed to change an existing initiative statute by adding or taking from it some particular provision. ( Proposition 103 Enforcement Project v. Quackenbush (1998) 64 Cal.App.4th 1473, 1485; Franchise Tax Bd. v. Cory (1978) 80 Cal.App.3d 772, 776.)

In Oluwa, the issue was whether defendant, who was sentenced to 15 years to life for second degree murder, was entitled to a more favorable credit calculation for postsentence worktime credits under section 2933. ( In re Oluwa, supra, 207 Cal.App.3d 439 .) In 1982, after the passage of the Briggs Initiative, the Legislature enacted section 2933 without voter approval. The Court of Appeal determined that the Briggs Initiative had adopted, by specific reference, the provisions contained in article 2.5 and incorporated those provisions in the form they existed at the time of the election and not in the form as subsequently modified. The court relied on a legislative analysis accompanying the initiative's ballot statement which specifically addressed the availability of conduct credits and advised voters that defendants sentenced to 15 years to life in prison would have to serve a minimum of 10 years before becoming eligible for parole. It concluded that the electorate clearly intended that a second degree murderer serve 10 years before parole consideration and that an application of the more liberal credits scheme under section 2933 would be contrary to the voter's intent. ( In re Oluwa, supra, at pp. 445-446.) The court reasoned, "The Legislature should not be permitted to do indirectly that which it cannot do directly." ( Id. at p. 446.)

In this case, the Court of Appeal recognized that, unlike the expansion of credits in Oluwa, the limitation of credits by section 2933.1 does not directly contradict the intention of the electorate in approving the Briggs Initiative. It nevertheless concluded that "the limitation of credits effects no less an amendment of section 190."

We disagree. To determine the meaning of a statute, we seek to discern the sense of its language, in full context, in light of its purpose. ( In re Cervera (2001) 24 Cal.4th 1073, 1077.) The relevant portion of former section 190, as approved by the Briggs Initiative, stated: "The provisions of Article 2.5 (commencing with Section 2930) of Chapter 7 of Title 1 of Part 3 of the Penal Code shall apply to reduce any minimum term of 25 or 15 years in state prison imposed pursuant to this section, but such person shall not otherwise be released on parole prior to such time." (Prop. 7, as approved by voters, Gen. Elec. (Nov. 7, 1978), reprinted at Deering's Ann. Pen. Code, supra, § 190, p. 82.) At the time the initiative was approved, article 2.5 contained only sections 2930, 2931, and 2932 ( In re Oluwa, supra, 207 Cal.App.3d at p. 445), provisions that only authorized the award of postsentence prison conduct credits. (See People v. Sage (1980) 26 Cal.3d 498, 504-506.) The provisions currently contained in article 2.5 continue to authorize only postsentence prison conduct credits. (See People v. Buckhalter, supra, 26 Cal.4th at p. 31; In re Cervera, supra, 24 Cal.4th at pp. 1078-1079; People v. Thomas (1999) 21 Cal.4th 1122, 1125 [under the "Three Strikes" law, statutory language referring to article 2.5 referred to postsentence, not presentence conduct credits]; People v. Goodloe (1995) 37 Cal.App.4th 485, 488-489.) Sections 2900.5 and 4019, which authorize the award of presentence conduct credits ( People v. Buckhalter, supra, 26 Cal.4th at pp. 30-32; People v. Goodloe, supra, 37 Cal.App.4th at p. 495), were and continue to be in a different article. (See pt. 3, tit. 1, ch. 7, art. 1; id., tit. 4, ch. 1; see also Notes, Deering's Ann. Pen. Code, supra, foll. § 2900.5, pp. 409-410, 411; id. (2001 supp.) foll. § 2900.5, p. 67; id. § 4019, p. 41.) Although section 2933.1 is currently contained in article 2.5, that section does not authorize the award of presentence conduct credits. It simply limits the presentence conduct credits authorized by section 4019. (See People v. Buckhalter, supra, 26 Cal.4th at pp. 31-32; People v. Thomas, supra, 21 Cal.4th at p. 1126.)

Thus, the first clause, in referring to the availability of credits under "Article 2.5 (commencing with Section 2930) . . . to reduce any minimum term" for those defendants sentenced under former section 190, was specifically referring only to the availability of postsentence conduct credits. This clause, authorizing the availability of postsentence conduct credits to reduce a murder term, when read together with the second clause, "but such person shall not otherwise be released on parole prior to such time," reflects the voters' intent to establish the absolute minimum prison term a convicted murderer must serve, after the award of the term-shortening postsentence conduct credits. (See People v. Jenkins (1995) 10 Cal.4th 234, 245, fn. 7 [Briggs Initiative established a minimum prison term a convicted murderer must serve].) As explained in Oluwa, the legislative analysis, accompanying the ballot statement, assured the voters that the award of article 2.5 postsentence conduct credits would reduce a sentence of 15 years to life to a minimum term of 10 years before parole eligibility. ( People v. Oluwa, supra, 207 Cal.App.3d at pp. 442-443.)

In arguing that the trial court's limitation of his presentence conduct credits was an improper legislative amendment, defendant assumes that he is entitled to full presentence conduct credits under section 4019. However, in determining electorate intent, we believe that the language of former section 190 presents an ambiguity. On the one hand, the phrase, "but such person shall not otherwise be released on parole prior to such time" (italics added), can be interpreted to impliedly prohibit the award of any conduct credits, other than postsentence conduct credits, to murderers. Under this construction, defendant is not entitled to any presentence conduct credits under section 4019.

On the other hand, another reasonable interpretation is that former section 190, in referring specifically to article 2.5 prison conduct credits, was addressing only the manner in which postsentence conduct credits can apply to reduce a murder sentence without any reference to presentence conduct credits. Because the statute does not preclude the award of presentence conduct credits to defendants convicted of murder, section 4019, which generally authorizes such credits, remains operative. Under this construction, defendant is not precluded from an award of presentence conduct credits under section 4019. This interpretation is consistent with the Attorney General's position. He concedes that convicted murderers whose cases fall into the window period between the effective dates of section 2933.1 and Proposition 222 are entitled to some presentence conduct credits. Moreover, because an ambiguity in the statutory language should be construed "'as favorably to the defendant as its language and the circumstances of its application may reasonably permit'" ( People v. Garcia (1999) 21 Cal.4th 1, 10), we adopt the latter construction. Consequently, because former section 190 does not specifically authorize or prohibit presentence conduct credits, any limitation of such credits against defendant's sentence, otherwise authorized by section 4019, is not an invalid modification of the Briggs Initiative. Oluwa is distinguishable because it involved the legislative amendment of article 2.5 postsentence conduct credits. (See People v. Aguirre, supra, 56 Cal.App.4th at p. 1140 ["[s]ection 2933 [is a] purely postsentence statute"].) Unlike Oluwa, here the trial court's restriction of presentence conduct credits under section 2933.1 is not inconsistent with former section 190 and does not otherwise circumvent the intent of the electorate in adopting the Briggs Initiative. (Cf. People v. Jenkins, supra, 10 Cal.4th at p. 245, fn. 7; People v. Ruiz (1996) 44 Cal.App.4th 1653, 1659-1661.) Therefore, the Court of Appeal erred in determining that the trial court improperly limited defendant's presentence conduct credits under section 2933.1.

Conclusion

We reverse the judgment of the Court of Appeal relating to the credits issue and remand the case to that court for further proceedings consistent with this opinion.

We Concur:

GEORGE, C.J.

KENNARD, J.

BAXTER, J.

WERDEGAR, J.

BROWN, J.

MORENO, J.