The opinion of the court was delivered by: Justice Thomas
The sole issue in this appeal is whether, under section 10(a) of the Public Safety Employee Benefits Act (Act) (820 ILCS 320/10 (West 2000)), the phrase "catastrophic injury" is synonymous with an injury resulting in a line-of-duty disability under section 4-110 of the Illinois Pension Code (Code) (40 ILCS 5/4-110 (West 2000)). We hold that it is.
Plaintiff, Bill Krohe, was a firefighter employed by defendant, the City of Bloomington. In June 2000, and pursuant to section 4-110 of the Code, the City's pension board awarded plaintiff a line-of-duty disability pension for injuries sustained in the line of duty. *fn1 Shortly thereafter, plaintiff asked the City to continue paying his and his family's health insurance premiums, as required by section 10(a). Insisting that section 10(a) did not mandate such payment, the City declined plaintiff's request. Plaintiff then filed a complaint for declaratory relief. The circuit court of McLean County ruled in plaintiff's favor and ordered the City to continue paying plaintiff's health insurance premiums. The City appealed, and, with one justice dissenting, the appellate court affirmed. 329 Ill. App. 3d 1133. We granted the City's petition for leave to appeal. 177 Ill. 2d R. 315(a).
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). If the statutory language is ambiguous, however, we may look to other sources to ascertain the legislature's intent. People v. Ross, 168 Ill. 2d 347, 352 (1995). 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).
"(a) An employer who employs a full-time *** firefighter, who *** suffers a catastrophic injury or is killed in the line of duty shall pay the entire premium of the employer's health insurance plan for the injured employee, the injured employee's spouse, and for each dependent child of the injured employee until the child reaches the age of majority ***." 820 ILCS 320/10(a) (West 2000).
The problem in this case arises from the fact that, although the legislature made section 10(a)'s application contingent upon the existence of a "catastrophic injury," the Act nowhere defines "catastrophic injury." The City maintains that the absence of a definition is of no consequence, however, as the phrase "catastrophic injury" unambiguously encompasses only those injuries that "severely limit the earning power of the affected employee." *fn2 Plaintiff counters that the phrase is "ambiguous, uncertain, and subjective" and that its meaning is ascertainable only by examining the Act's legislative history.
We agree with plaintiff. As used in section 10(a), the phrase "catastrophic injury" is ambiguous. A statute is ambiguous if it is capable of being understood by reasonably well-informed persons in two or more different ways. People v. Jameson, 162 Ill. 2d 282, 288 (1994). In this case, "reasonably well-informed persons" have tendered no less than six distinct definitions of "catastrophic injury," all of which purport to vindicate the legislature's intent.
As mentioned above, the City initially argues that the phrase "catastrophic injury" encompasses only those injuries that "severely limit the earning power of the affected employee." (Emphasis added.) Elsewhere in its brief, the City contends that "a reasonable interpretation of [section 10(a)] is that the catastrophic injury be of such a nature that the firefighter is precluded, as a result of a line-of-duty injury, from obtaining gainful employment elsewhere which provides a salary comparable to that of a firefighter." (Emphasis added.) The City then endorses yet a third construction of "catastrophic injury," that articulated by the appellate court in Villarreal v. Village of Schaumburg, 325 Ill. App. 3d 1157 (2001). In Villarreal, the court held that a "catastrophic injury" is one that is "financially ruinous," rendering a firefighter "incapable of engaging in any gainful employment." (Emphasis in original.) Villarreal, 325 Ill. App. 3d at 1163. In his dissent below, Justice Steigmann posits that "whatever it means, it means something more than a duty-related injury which qualifies a firefighter for a line-of-duty disability pension." (Emphasis added.) 329 Ill. App. 3d at 1141 (Steigmann, J., dissenting). The Villages of Schaumburg and Skokie, as amicus in this appeal, maintain that catastrophic injuries are those "that approach a life-threatening status and/or that interfere with an individual's earning capacity." (Emphasis added.) Finally, both plaintiff and the Associated Firefighters of Illinois, as amicus, insist that any injury that renders a person permanently unable to engage in his or her chosen profession is, by definition, "catastrophic."
Significantly, not one of the six definitions set forth above relies exclusively upon section 10(a)'s plain language. On the contrary, the definitions advanced by or in support of the City derive from four distinct dictionary definitions of "catastrophe," as well as from statutory definitions borrowed from other jurisdictions. Similarly, the definitions advanced by or in support of plaintiff come not from section 10(a) itself but from section 10(a)'s legislative history. And while all of these definitions are to some degree "reasonable," none of them are either compelled or foreclosed by the statute's plain language. We therefore hold that the phrase "catastrophic injury," as used in section 10(a), is ambiguous.
In reaching this result, we note that even the definitions proffered by the City do nothing to resolve section 10's ambiguity, as they fail to identify with any degree of certainty or predictability what types of injuries qualify as "catastrophic." Indeed, one point on which plaintiff and the City agree is that blindness and loss of limb are textbook examples of "catastrophic" injuries under section 10(a). Yet neither blindness nor loss of limb renders a firefighter "incapable of engaging in any gainful employment," which the City at one point insists is the sine qua non of a "catastrophic injury." Nor do these injuries necessarily preclude a firefighter from "obtaining gainful employment elsewhere which provides a salary comparable to that of a firefighter," the City's alternative standard for evaluating whether an injury is "catastrophic." At the same time, however, both blindness and loss of limb instantly terminate a firefighter's ability to pursue his chosen profession, a definition of "catastrophic" that plaintiff endorses but the City categorically rejects. Thus, even as defined by the City, "catastrophic injury" remains steadfastly ambiguous.
Because the phrase "catastrophic injury" is ambiguous, we may look beyond the Act's language to ascertain its meaning. In re D.D., 196 Ill. 2d 405, 419 (2001). To this end, a statute's legislative history and debates are "[v]aluable construction aids in interpreting an ambiguous ...