delivered the opinion of the court:
Plaintiffs, Jack and Margaret Caveney, are shareholders in Panduit Corporation. For the tax years ending December 31, 1993, 1994, and 1995, Panduit elected to be treated as a subchapter S corporation for federal and state tax purposes. During the tax years in question, plaintiffs claimed a credit against their Illinois income tax liability, pursuant to section 201(k) of the Illinois Income Tax Act (the Act) (35 ILCS 5/20l(k) (West 1996)), for research and development expenditures incurred by Panduit. The State disallowed the claims and calculated back taxes and interest in the amount of $1,091,131.60, which plaintiffs paid under protest.
Seeking a return of the amounts paid under protest, plaintiffs filed suit under the State Officers and Employees Money Disposition Act (30 ILCS 230/1 et seq. (West 2000)). Plaintiffs first argued that they qualified for the tax credit under the version of section 201(k) that was in force during the tax years in question. In the alternative, plaintiffs argued that, if they did not so qualify, section 201(k) violated the uniformity clause of the Illinois Constitution (Ill. Const. 1970, art. IX, § 2). The circuit court of Du Page County agreed with both of plaintiffs’ arguments and entered summary judgment in plaintiffs’ favor. The State appealed.
Before the appellate court, plaintiffs not only repeated their previous arguments but also argued for the first time that they qualified for the research and development tax credit under a 1999 amendment to section 201(k), which was enacted as part of Public Act 91 — 644 (Pub. Act 91 — 644, eff. August 20, 1999). The appellate court affirmed solely on the basis of the 1999 amendment. Citing this court’s decision in First of America Trust Co. v. Armstead, 171 Ill. 2d 282 (1996), the appellate court explained that retroactive application of the 1999 amendment was appropriate because the State had failed to identify any “vested right” that would be compromised by such an application.
The State filed a petition for leave to appeal (177 Ill. 2d R. 315(a)), and this court issued a supervisory order vacating the appellate court’s judgment and remanding the cause for reconsideration in light of Commonwealth Edison Co. v. Will County Collector, 196 Ill. 2d 27, 37 (2001). Caveney v. Bower, 195 Ill. 2d 549 (2001) (supervisory order). On remand, and with one justice dissenting, the appellate court again affirmed the entry of summary judgment in plaintiffs’ favor. 326 Ill. App. 3d 1. We granted the State’s petition for leave to appeal. 177 Ill. 2d R. 315(a).
ANALYSIS
Motion to Strike
At the outset, we must address plaintiffs’ motion to strike certain portions of the State’s opening brief. In that brief, the State argued not only that the 1999 amendment to section 201(k) does not apply retroactively but also that (1) plaintiffs do not qualify for the research and development tax credit under the previous version of section 201(k), and (2) the previous version of section 201(k) does not violate the uniformity clause of the Illinois Constitution. Citing Supreme Court Rule 315(b)(3) (177 Ill. 2d R. 315(b)(3)), plaintiffs argue that we must strike those portions of the State’s brief that address the latter two arguments, as those arguments were neither addressed by the appellate court nor asserted in the State’s petition for leave to appeal as a basis for reversing the appellate court’s judgment.
Plaintiffs’ motion is utterly without merit. First, the State clearly preserved these issues for review. The contested arguments were fully briefed and argued in both the trial court and the appellate court. The appellate court’s decision to affirm on other grounds does not amount to a procedural default by the State. Second, the State could not have asserted the contested arguments as a basis for reversing the appellate court’s judgment because, as plaintiffs concede in their motion, the appellate court did not reach these issues. Although these issues formed the basis for the trial court’s decision, the appellate court affirmed on a wholly different basis, namely, the retroactive application of the 1999 amendment. Given that the retroactive application of the 1999 amendment was the only issue addressed in the appellate court’s decision, it is only natural that that issue constituted the State’s sole basis for reversing that decision. Finally, and contrary to representations contained in plaintiffs’ motion, the State did raise the contested arguments in its petition for leave to appeal. The following footnote appears on page 15 of the State’s petition for leave to appeal:
“The Caveneys, of course, have maintained that they were entitled to the tax credits even under the preamendment version of section 201(k). The petitioners have taken the opposite position. The appellate court has never reached the issue, twice deciding the case on the ground that the 1999 amendment was retroactive. If this court grants leave to appeal, the petitioners would naturally raise the tax issue in addition to the issue of retroactivity. The petitioners do not raise the tax issue as a ground for leave to appeal because the appellate court never decided the issue.” (Emphasis added.)
In this footnote, the State did all it reasonably could be expected to do with respect to the contested arguments, which were unavailable to the State as bases for reversing the appellate court’s judgment yet remained wholly available to plaintiffs as bases for affirming the appellate court’s judgment. See Schultz v. Northeast Illinois Regional Commuter R.R. Corp., 201 Ill. 2d 260, 281 (2002) (appellate court’s judgment may be affirmed on any basis in the record). Plaintiffs’ motion to strike is denied.
Section 201(k): Original Version
Turning to the merits, we first address whether plaintiffs qualify for the research and development tax credit under the version of section 201(k) that existed prior to the 1999 amendment. Relying upon the statute’s plain language, the State insists that, as Panduit’s shareholders, plaintiffs may not personally claim a tax credit for research and development expenses actually incurred by Panduit. Plaintiffs counter that, given both the nature of subchapter S corporations and the clear public policy underlying section 201(k), the legislature must have intended to make the research and development tax credit available to S corporation shareholders. We agree with the State.
The fundamental rule of statutory construction is to ascertain and give effect to the legislature’s intent. Michigan Avenue National Bank v. County of Cook, 191 Ill. 2d 493, 503-04 (2000). The best indication of legislative intent is the statutory language, given its plain and ordinary meaning. Illinois Graphics Co. v. Nickum, 159 Ill. 2d 469, 479 (1994). Where the language is clear and unambiguous, we must apply the statute without resort to further aids of statutory construction. Davis v. Toshiba Machine Co., America, 186 Ill. 2d 181, 184-85 (1999). The construction of a statute is a question of law that is reviewed de novo. In re Estate of Dierkes, 191 Ill. 2d 326, 330 (2000).
Prior to the 1999 amendment, section 201(k) provided:
“Beginning with tax years ending after July 1, 1990, a taxpayer shall be allowed a credit against the tax imposed by subsections (a) and (b) of this Section for increasing research activities in this State. The credit allowed against the tax imposed by subsections (a) and (b) shall be equal to 6V2% of the qualifying expenditures for increasing research activities in this State.” 35 ILCS 5/201(k) (West 1998).
For purposes of section 201(k), “qualifying expenditures” are defined as “the qualifying expenditures as defined for the federal credit for increasing research activities which would be allowable under Section 41 of the Internal Revenue Code and which are conducted in this State.” 35 ILCS 5/20 l(k) (West 1998). Section 41 of the Internal Revenue Code, in turn, defines “qualified research expenses” as those that “are paid or incurred by the taxpayer during the taxable year in carrying on any trade or business of the taxpayer.” (Emphasis added.) 26 U.S.C. § 41(b)(1) (2000). The “tax imposed by subsections (a) and (b)” is the Illinois income tax. 35 ILCS 5/201(a), (b) (West 1998).
We find no ambiguity in the foregoing statute and conclude that plaintiffs are ineligible for the research and development tax credit that existed prior to the 1999 amendment. Prior to that amendment, section 201(k) authorized a credit only against the taxpayer’s Illinois income tax liability and only for research and development expenses actually incurred by the taxpayer. Here, there is no question that the expenses in question were incurred by Panduit and not by plaintiffs personally. Panduit, however, may not claim a credit for these expenses, as Panduit is a subchapter S corporation and therefore exempt from the Illinois income tax. See 35 ILCS 5/205(c) (West 2000). By the same token, plaintiffs are ineligible for the credit because, although they are subject to the Illinois income tax, they did not personally incur the expenses. To be sure, had plaintiffs personally incurred any qualifying expenses during the years in question, they could have claimed a credit for those expenses in accordance with section 201(k). What plaintiffs could not do, however, is claim a credit against their personal income tax liability for qualifying expenses incurred by a third party, even if that third party was an S corporation of which plaintiffs are shareholders.
This conclusion is supported by the fact that, when the legislature originally enacted section 201(k) in 1990, section 201 already included two tax credit provisions that did authorize S corporation shareholders to claim a credit against their personal Illinois income tax liability for expenses incurred by the S corporation. Section 201(f)(1), which establishes an income tax credit for investments in designated “Enterprise Zones,” specifically provides that:
“For *** shareholders of Subchapter S corporationsf ] there shall be allowed a credit under this subsection (f) to be determined in accordance with the determination of income and distributive share of income under Sections 702 and 704 and Subchapter S of the Internal Revenue Code.” 35 ILCS 5/201(f)(l) (West 1992).
Section 201(j), which authorizes an income tax credit for certain educational and vocation training expenses, contains the identical pass-through provision. 35 ILCS 5/201Q) (West 1992). Significantly, sections 201(f)(1) and 201(j) were enacted five years prior to the enactment of section 201(k). Conversely, even after enactment of the 1999 amendment to section 201(k), section 201 continues to include tax credit provisions that do not include pass-through provisions. See, e.g., 35 ILCS 5/201(h), (1) (West 2000). Of course, it is well established that, when the legislature uses certain language in one part of a statute and different language in another, this court will presume that different results were intended. In re K.C., 186 Ill. 2d 542, 549-50 (1999). Thus, we may presume that the legislature’s failure to include a pass-through provision in the original version of section 201(k) was deliberate, and that the original version of section 201(k) was never meant to apply to S corporation shareholders. Moreover, were we to agree with plaintiffs and hold that section 201(k)’s tax credit passed through to S corporation shareholders even before the 1999 amendment, the pass-through provisions contained in sections 201(f)(1) and 201(j) would be rendered “meaningless surplusage.” We therefore will not adopt such a reading. See In re K.C., 186 Ill. 2d at 550.
Section 201(k): Amended Version
We next consider whether plaintiffs qualify for the research and development tax credit under the 1999 amendment to section 201(k). Under that amendment, which was enacted as part of Public Act 91 — 644 (Pub. Act 91 — 644, eff. August 20, 1999), the legislature added the following pass-through provision to section 201(k), thereby specifically extending section 201(k)’s benefits to S corporation shareholders:
“For partners, shareholders of subchapter S corporations, and owners of limited liability companies, if the liability company is treated as a partnership for purposes of federal and State income taxation, there shall be allowed a credit under this subsection to be determined in accordance with the determination of income and distributive share of income under Sections 702 and 704 and subchapter S of the Internal Revenue Code.” 35 ILCS 5/201(k) (West 2000).
Plaintiffs insist that, although this amendment was enacted in 1999, it nevertheless applies retroactively because the State does not a possess a “vested right” to collect taxes owed under the prior version of the law. The State disagrees, arguing that, under this court’s recent decision in Commonwealth Edison Co. v. Will County Collector, 196 Ill. 2d 27 (2001), retroactive application of the amendment is prohibited because such an application would attach new legal consequences to previously completed acts. We agree with the State, but we do so for different reasons.
In Commonwealth Edison, this court for the first time adopted the United States Supreme Court’s retroactivity analysis, as set forth in Landgraf v. USI Film Products, 511 U.S. 244, 128 L. Ed. 2d 229, 114 S. Ct. 1483 (1994). Under the Landgraf analysis, as adopted by this court, the first question is whether the legislature has clearly indicated the temporal reach of an amended statute. Commonwealth Edison, 196 Ill. 2d at 38. If so, then, absent a constitutional prohibition, that expression of legislative intent must be given effect. Commonwealth Edison, 196 Ill. 2d at 38. If not, then the court must determine whether applying the statute would have a retroactive impact, i.e., whether it would impair rights a party possessed when he acted, increase a party’s liability for past conduct, or impose new duties with respect to transactions already completed. Commonwealth Edison, 196 Ill. 2d at 38. If there would be no retroactive impact, then the amended law may be applied retroactively. Commonwealth Edison, 196 Ill. 2d at 38. If there would be a retroactive impact, however, then the court must presume that the legislature did not intend that it be so applied. Commonwealth Edison, 196 Ill. 2d at 38.
As it turns out, despite the analytical challenges typically posed by a phrase like “retroactive impact,” application of the Landgraf approach in Illinois should prove uneventful. This is because, as this court recently acknowledged in People v. Glisson, 202 Ill. 2d 499 (2002), the legislature has clearly indicated the “temporal reach” of every amended statute. In section 4 of the Statute on Statutes (5 ILCS 70/4 (West 2000)), which this court describes as “the general saving clause of Illinois” (Glisson, 202 Ill. 2d at 505), the legislature mandated that:
“No new law shall be construed to repeal a former law, whether such former law is expressly repealed or not, as to any offense committed against the former law, or as to any act done, any penalty, forfeiture or punishment incurred, or any right accrued, or claim arising under the former law, or in any way whatever to affect any such offense or act so committed or done, or any penalty, forfeiture or punishment so incurred, or any right accrued, or claim arising before the new law takes effect, save only that the proceedings thereafter shall conform, so far as practicable, to the laws in force at the time of such proceeding.” 5 ILCS 70/4 (West 2000).
In Glisson, this court construed the foregoing language as authorizing the “retroactive application of amendments or repeals in criminal statutes *** only if such changes are procedural in nature.” Glisson, 202 Ill. 2d at 507. Conversely, section 4 “forbids retroactive application of substantive changes to statutes.” Glisson, 202 Ill. 2d at 507. Thus, section 4 represents a clear legislative directive as to the temporal reach of statutory amendments and repeals: those that are procedural in nature may be applied retroactively, while those that are substantive may not.
Of course, in Glisson, we spoke only of “amendments or repeals in criminal statutes” (emphasis added) (Glisson, 202 Ill. 2d at 507), whereas the present case is clearly a civil matter. This is of no consequence, however, as nothing on the face of section 4 confines its application to criminal statutes.1 More importantly, this court has never hesitated to utilize section 4 in ascertaining the temporal reach of a civil statute. In fact, in a case nearly identical to the present appeal, this court held that section 4 precludes the retroactive application of a recently enacted tax benefit, as such a measure is clearly substantive in nature. See Connell v. Crosby, 210 Ill. 380 (1904).
In Connell, the decedent’s will provided that a certain portion of his estate be devoted to the founding of a college. At the time of the decedent’s death in 1897, bequests for educational purposes were subject to the Illinois inheritance tax. In 1901, and before a petition for the collection of decedent’s estate taxes had been filed, the legislature amended the Inheritance Tax Act to exempt bequests for educational purposes. In rejecting the executor’s argument that the 1901 exemption should apply retroactively to the decedent’s educational bequest, this court explained:
“The amendatory act of 1901 does not, in terms, repeal the former act. It contains no saving clause, nor does it in terms purport to affect, in any way, any right, whether vested or inchoate, which might then exist. Section 4 of chapter 131 (Hurd’s Stat. 1899, p. 1650) furnishes the guide for determining the effect to he given the amendatory enactment. That section provides: ‘No new law shall be construed to repeal a former law, whether such former law is expressly repealed or not, as to any *** right accrued or claim arising under the former law, or in any way whatever to affect *** any right accrued or claim arising before the new law takes effect, save only that the proceedings thereafter shall conform, so far as practicable, to the laws in force at the time of such proceedings.’ It is to be assumed the amendatory act was framed in view of the provisions of said section 4 of chapter 131, and that it was the legislative intent the amendatory act should have prospective operation, only. Statutes declaring the effect of or the construction to be given subsequently enacted repealing acts will be deemed operative and effective by the courts unless a contrary intent is plainly manifested in the later enactment. [Citations.] The right which accrued or the claim which arose to the tax, under the statute in force at the time of the death of the testator, was therefore unaffected, and remained enforcible notwithstanding the subsequent enactment exempting bequests for educational purposes from the tax. [Citations.]” Connell, 210 Ill. at 386-87.
Significantly, section 4 reads exactly the same today as it did on July 1, 1874, the day it was enacted.
In light of section 4, the Landgraf analysis in Illinois becomes quite simple. Indeed, with respect to a statutory amendment or repeal, it is virtually inconceivable that an Illinois court will ever go beyond step one of the Landgraf approach. Again, step one requires a court to ascertain whether the legislature has clearly indicated the temporal reach of the amended statute. Commonwealth Edison, 196 Ill. 2d at 38. If so, then, absent a constitutional prohibition, that expression of legislative intent must be given effect. Such was the case in Commonwealth Edison, where this court concluded that the amendatory act at issue contained an “unequivocal expression of legislative intent” authorizing retroactive application. Commonwealth Edison, 196 Ill. 2d at 42. If the amendatory act does not contain a clear indication of legislative intent, then “[i]t is to be assumed the amendatory act was framed in view of the provisions of said section 4.” Connell, 210 Ill. at 386. Again, “[sjtatutes declaring the effect of or the construction to be given subsequently enacted repealing acts will be deemed operative and effective by the courts unless a contrary intent is plainly manifested in the later enactment.” (Emphasis added.) Connell, 210 Ill. at 387; see also Commonwealth Edison, 196 Ill. 2d at 38 (“if the legislature has clearly indicated what the temporal reach of an amended statute should be, then *** that expression of legislative intent must be given effect”). As Glisson teaches, section 4 represents a clear legislative indication that the retroactive application of substantive statutory changes is forbidden. Thus, for purposes of Landgraf s first step, the legislature always will have clearly indicated the temporal reach of an amended statute, either expressly in the new legislative enactment or by default in section 4 of the Statute on Statutes.
Turning back to the question at hand, then, we must decide whether the 1999 amendment to section 201(k) may be applied retroactively to plaintiffs’ 1993, 1994, and 1995 research and development expenditures. Our first task, of course, is to ascertain whether the legislature has clearly indicated the temporal reach of the 1999 amendment. See Commonwealth Edison, 196 Ill. 2d at 38. Unquestionably, it has. Unlike in Commonwealth Edison, however, the legislature’s clear indication is not found in the amendatory act itself. Indeed, the 1999 amendment to section 201(k) specifically states that “[n]o inference shall be drawn from this amendatory Act *** in construing this Section for taxable years beginning before January 1, 1999.” 35 ILCS 5/20l(k) (West 2000). Rather, the legislature’s clear pronouncement is found in section 4 of the Statute on Statutes, which “forbids retroactive application of substantive changes to statutes.” Glisson, 202 Ill. 2d at 506-07. Clearly, the 1999 amendment to section 201(k) is a substantive change in the law, as it establishes an income tax credit for S corporation shareholders that previously did not exist. This being the case, “[i]t is to be assumed the amendatory act was framed in view of the provisions of said section 4 ***, and that it was the legislative intent the amendatory act should have prospective operation, only.” See Connell, 210 Ill. at 386-87.
Uniformity Clause
Finally, we are asked to consider whether the version of section 201(k) that existed prior to the 1999 amendment violates the uniformity clause of the Illinois Constitution. See Ill. Const. 1970, art. IX, § 2. We hold that it does not.
The uniformity clause of the Illinois Constitution provides as follows:
“In any law classifying the subjects or objects of non-property taxes or fees, the classes shall be reasonable and the subjects and objects within each class shall be taxed uniformly. Exemptions, deductions, credits, refunds and other allowances shall be reasonable.” Ill. Const. 1970, art. IX, §2.
In light of the foregoing language, we are hard pressed to identify even the basis for a uniformity challenge to the preamended version of section 201(k). The gravamen of a uniformity clause challenge is a classification, and the preamended version of section 201(k) contains no such thing. Prior to the 1999 amendment, section 201(k) granted all taxpayers subject to the income tax a credit for qualifying research and development expenditures incurred by the taxpayer. Such a credit is perfectly uniform. In fact, the first and only time a classification crept into section 201(k) was in 1999, when the legislature authorized only certain classes of Illinois income taxpayers to claim a credit for qualifying research and development expenditures incurred not by the taxpayer but by a third party. As this classification does not form the basis of the uniformity challenge in this case, however, we need not explore this issue any further.
CONCLUSION
For the foregoing reasons, the judgments of the appellate court and the circuit court are reversed, and the cause is remanded to the circuit court with directions to enter summary judgment for the State.
Judgments reversed; cause remanded with directions.
To be sure, in West’s edition of the Illinois Compiled Statutes section 4 bears the title, “Rights, etc., saved — Criminal cases— Application of new law by consent.” (Emphasis added.) 5 ILCS 70/4 (West 2000). This title, however, represents an unofficial, publisher-generated caption and therefore is wholly irrelevant in construing the scope of section 4. See Michigan Avenue National Bank v. County of Cook, 191 Ill. 2d 493, 506 (2000).