We say "generally" because if the legislature has charged an agency with administering and enforcing a statute, we "will give substantial weight and deference" to the agency's resolution of any ambiguities in that statute — even if the ambiguity concerns the extent of the agency's jurisdiction under that statute. Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n, 95 Ill. 2d 142, 152, 447 N.E.2d 295, 300 (1983). In Illinois Consolidated Telephone Co., 95 Ill. 2d at 145-46, 447 N.E.2d at 296, for instance, the issue was whether the definition of "public utility" in section 10.3(b) of the Act (Ill. Rev. Stat. 1979, ch. 111 2/3, par. 10.3(b)) gave the Commission authority to regulate radio paging.

In support of its contention, First Page cites cases involving the question whether a paging company is a public utility for regulatory purposes. First Page cites in particular the following: Zachs v. Groppo, 207 Conn. 683, 542 A.2d 1145 (1988); Illinois Cons. Telephone Co. v. Ill. Commerce Com., 95 Ill.2d 142, 447 N.E.2d 295 (1983); and Radio Relay Corp. v. Pub. Util. Comm., 45 Ohio St.2d 121, 341 N.E.2d 826 (1976). The issue in the Connecticut case involved taxation.

Indeed, "if the legislature has charged an agency with administering and enforcing a statute, we `will give substantial weight and deference' to the agency's resolution of any ambiguities in that statute — even if the ambiguity concerns the extent of the agency's jurisdiction under that statute." Illinois Bell Telephone Co. v. Illinois Commerce Comm'n, 362 Ill. App. 3d 652, 656 (2005), quoting Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n, 95 Ill. 2d 142, 152 (1983). As our supreme court has made clear, "`the general principle of judicial deference to administrative interpretation applies in full strength where such interpretation involves resolution of jurisdictional questions.'"

• 2 In addition, courts give substantial weight and deference to the interpretation of a statute by the agency charged with the administration and enforcement of that statute. ( Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n (1983), 95 Ill.2d 142, 447 N.E.2d 295.) A significant reason for this deference is that courts appreciate that agencies such as the Board can make informed judgments based upon their experience and expertise. ( Illinois Consolidated Telephone, 95 Ill.2d at 153, 447 N.E.2d at 300.) Interpretations by administrative agencies express an informed source for ascertaining legislative intent.

We recognize that our interpretation of the Human Rights Act is at odds with that of the Commission. Where based on agency expertise, the interpretation of an ambiguous statute by an agency charged with its administration is generally entitled to deference. Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n, 95 Ill.2d 142, 152 (1983). However, the erroneous construction of a statute by an administrative agency is not binding on this court.

The courts give substantial weight and deference to a reasonable construction of an ambiguous statute by the governmental department charged with enforcement of the statute. ( People ex rel. Watson v. House of Vision (1974), 59 Ill.2d 508, 514-15; Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n (1983), 95 Ill.2d 142, 152.) Interpretations of statutes by administrative agencies are sources for ascertaining legislative intent.

(See, e.g., In re Petition of the Galesburg Sanitary District to Amend Regulations (1983), 52 Ill. P.C.B. Op. 299; In re Proposed Water Quality Standard for Wood River (1982), 49 Ill. P.C.B. Op. 307; In re Proposed Amendments to Rule 203.1 of the Water Pollution Regulations (1978), 29 Ill. P.C.B. Op. 395.) Courts will give substantial deference to the interpretation of a statute by the agency charged with its administration and enforcement ( Illinois Consolidated Telephone Co. v. Illinois Commerce Com. (1983), 95 Ill.2d 142, 152), particularly where the administrative interpretation has been long standing ( 95 Ill.2d 142, 153). The Board has always interpreted the language in section 27 as a grant of authority to adopt site-specific standards, and we find this interpretation to be well founded.

(Emphasis added.) Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n , 95 Ill. 2d 142, 152, 69 Ill.Dec. 78, 447 N.E.2d 295 (1983). Statutory ambiguity is a prerequisite to this duty of deference.

However, courts appreciate an agency's experience and expertise in a given area and therefore will give substantial deference to its interpretation of an ambiguous statute it administers and enforces. Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n, 95 Ill.2d 142, 152–53, 69 Ill.Dec. 78, 447 N.E.2d 295 (1983). While not binding on the courts, an agency's interpretations are an informed source for ascertaining the legislature's intent in enacting the statute.

United Cities Gas Co. v. Illinois Commerce Comm'n, 163 Ill. 2d 1, 11 (1994). Though we are not bound by the Commission on questions of law ( Business Professional People for the Public Interest v. Illinois Commerce Comm'n, 136 Ill. 2d 192, 204 (1989)), we "will give substantial weight and deference to an interpretation of an ambiguous statute by the agency charged with the administration and enforcement of the statute" ( Illinois Consolidated Telephone Co. v. Illinois Commerce Comm'n, 95 Ill. 2d 142, 152 (1983)), which in this case is the Commission. Our review is limited to the following matters: (1) whether the Commission acted within its authority; (2) whether it made adequate findings to support its decision; (3) whether the decision was supported by substantial evidence; and (4) whether state or federal constitutional rights were infringed.