OPINION
CORNYN, Justice.This case comes to us on a certified question from the United States Court of Appeals for the Fifth Circuit. The question is whether a promissory note requiring interest to be charged at a rate that can be determined only by reference to a bank’s published prime rate is a negotiable instrument as defined by the Texas Uniform Commercial Code. Ackerman v. Federal Deposit Ins. Corp., 930 F.2d 3, 4 (5th Cir. 1991), certified question accepted sub nom., Amberboy v. Societe de Banque Privee, 34 Tex.Sup.Ct.J. 690 (June 22, 1991). For the reasons set forth below, we answer the question in the affirmative.
In Texas, negotiable instruments are governed by the Uniform Commercial Code (“U.C.C.”) as adopted by the Texas Legislature and codified in the Texas Business and Commerce Code.1 Specifically, section 3.104 contains the requirements of a negotiable instrument. That section provides:
(a) Any writing to be a negotiable instrument within this chapter must
(1) be signed by the maker or drawer; and
(2) contain an unconditional promise or order to pay a sum certain in money and no other promise, order, obligation or power given by the maker or drawer except as authorized by this chapter; and
(3) be payable on demand or at a definite time; and
(4) be payable to order or to bearer.
Tex.Bus. & Com.Code § 3.104. The Code does not define the term “sum certain.” However, section 3.106 lists several instances when the sum certain requirement is not defeated even though the amount payable is not explicitly stated on the instrument.2
*794This is not just an ordinary case of statutory construction. Our construction of the provisions of the U.C.C. is grounded in the Code’s fundamental purpose, which is to “simplify, clarify and modernize the law governing commercial transactions.... ” Tex.Bus. & Com.Code § 1.102(b)(1). Further, the drafters of the U.C.C. expressly contemplated that the courts would advance the basic purpose of the Code by construing the U.C.C.’s provisions “in the light of unforeseen and new circumstances and practices.” Tex.Bus. & Com.Code Ann. § 1.102, comment 1 (Vernon 1968); see also Gary B. Tillman, Variable Interest Rates, Negotiability, and the Sum Certain Requirement, 22 U.C.C. L.J. 36, 60 (1989). This “permit[s] the continued expansion of commercial practices through custom, usage and agreement of the parties.... ” Tex.Bus. & Com.Code § 1.102(b)(2).
It is our task to construe the U.C.C.’s “four corners” rule for determining whether the sum certain requirement is met. For an instrument to be negotiable under that rule, the sum certain to be paid must be capable of computation “from the instrument itself without reference to any outside source_” Tex.Bus. & Com.Code Ann. § 3.106, comment 1 (Vernon 1968). However, the Code itself evidences that this is not intended to be a rigid, absolute rule. Section 3.106 lists several instances in which reference to sources outside the instrument are necessary to determine the sum payable under the instrument. See, e.g., § 3.106(a)(4) (payment in exchange at current rate).
Section 3.106 does not explicitly mention variable rate notes (“VRNs”) because when the U.C.C. was developed in the 1950s and adopted in the 1960s, VRNs were virtually unknown. Fred H. Miller, 1990 Articles 3 and 4: Looking to the Twenty-First Century, UCC BULL., June 1991, at 1; Tillman, 22 U.C.C. L.J. at 61-62; see also Janine S. Hiller, Negotiability and Variable Interest Rates, 90 COM.L.J. 277, 277-78 (1985). The necessity for VRNs came about as a result of the volatile financial markets of the late 1970s. By the mid-1980s, VRNs accounted for 60% of the total loans made in this country. Hiller, 90 COM.L.J. at 277. That dominance in the financial markets has continued into the 90s. Federal Reserve, Statistical Release, Survey of Terms of Bank Lending Made During November 5-9,1990 (Dec. 14, 1990).
The majority of courts which have addressed the issue before us have declined to hold that notes which contain variable interest rates are negotiable instruments. Chemical Bank v. D3J Assocs. Ltd. Partnership, 14 U.C.C.Rep.Serv.2d (Callaghan) 790, 794, 1991 WL 58049 (D.Md.1991) (rate stated as 1% above floating prime or its equivalent charged by specified bank); In re Gas Reclamation, Inc. Securities Litigation, 741 F.Supp. 1094, 1102-03 (S.D.N.Y.1990) (rate stated as lesser of a fixed rate over the prime rate charged by a specified bank or the maximum lawful allowed), appeal dism’d sub nom. Abish v. Northwestern Nat’l Ins. Co., 924 F.2d 448 (2d Cir.1991); National Union Fire Ins. Co. v. Alexander, 728 F.Supp. 192, 199-200 (S.D.N.Y.1989) (rate stated as 2% above prime rate charged by Cullen Frost Bank, adjusted daily); Northern Trust Co. v. E.T. Clancy Export Corp., 612 F.Supp. 712, 715 (N.D.Ill.1985) (rate stated as ½% above the bank’s floating prime rate); Centerre Bank v. Campbell, 744 S.W.2d 490, 498 (Mo.App.1988) (interest may vary with bank rates charged to the lender); Taylor v. Boeder, 234 Va. 99, 360 S.E.2d 191, 195 (1987) (rate stated as 3% over Chase Manhattan prime adjusted monthly); Farmers Prod. Credit Ass’n v. Arena, 145 Vt. 20, 481 A.2d 1064, 1065 (1984) (provided for a variable rate of interest); A. Alport & Son, *795Inc. v. Hotel Evans, Inc., 65 Misc.2d 374, 317 N.Y.S.2d 937, 939-40 (1970) (provided for interest at bank rates). A number of states, either in response to court decisions which reject VRNs as negotiable instruments or for reasons that are not readily apparent, have amended section 3.106 to provide that the sum certain requirement is not defeated because the rate of interest to be charged is tied to and varies with certain enumerated types of published rates.3 A similar amendment to the Texas Uniform Commercial Code was contained in House Bill 2497, which passed the House but was not voted upon in the Senate.4
We believe the better reasoned view is reflected in the opinions of those courts which have held that VRNs do meet the sum certain requirement and thus are negotiable instruments subject to the terms of article 3 of the U.C.C. Goss v. Trinity Sav. & Loan Ass’n, 813 P.2d 492, 499 (Okla.1991) (interest rate tied to T-bill index); Tanenbaum v. Agri-Capital, Inc., 885 F.2d 464, 468-69 (8th Cir.1989) (applying the Texas Uniform Commercial Code); First City Fed. Sav. Bank v. Bhogaonker, 715 F.Supp. 1216, 1219-20 (S.D.N.Y.1989); Klehm v. Grecian Chalet, Ltd., 164 Ill.App.3d 610, 115 Ill.Dec. 662, 667, 518 N.E.2d 187, 192 (1987). Notably, four of the six states whose courts have held VRNs to be non-negotiable under versions of the U.C.C. similar to ours, all but Illinois5 and Vermont, have amended their versions of the U.C.C. to render VRNs negotiable.6 Paradoxically, the concurrent *796enactment of statutory amendments designed to “clarify existing law” and conflicting court decisions expounding on “existing law” prompted the National Conference of Commissioners on Uniform State Law to propose, in the interest of uniformity, its own amendments to article 3 of the Uniform Commercial Code to specifically provide that VRNs are negotiable instruments.7
A VRN which contains provision for interest to be paid at a variable rate that is readily ascertainable by reference to a bank’s published prime rate is compatible with the Code’s objective of commercial certainty. The Code does not require “mathematical certainty” but only “commercial certainty.” Tanenbaum, 885 F.2d at 468 (applying Tex.Bus. & Com.Code § 3.104 and citing Cudahy Packing Co. v. State Nat’l Bank, 134 F. 538, 542 (8th Cir.1904)). Commercial certainty serves the purpose of the law of negotiable instruments, which is to make the instrument the functional equivalent of money. Hiller, 90 COM.L.J. at 279; see also Cobb Bank & Trust Co. v. American Mfg. Mut. Ins. Co., 459 F.Supp. 328, 333 (N.D.Ga.1978). If the rate of interest to be paid under the instrument is readily ascertainable by reference to a bank’s published prime rate, this purpose is achieved.
We believe that the construction more consistent with the stated purpose of the U.C.C. and modern commercial practices obliges us to answer the Fifth Circuit’s certified question affirmatively. Widespread use and acceptance of VRNs in the 1980s is precisely the type of new circumstance contemplated by the drafters of section 1.102, comment 1.
Appellants’ reliance on our decision in Brazos River Authority v. Carr is misplaced. 405 S.W.2d 689 (Tex.1966). Although the bonds in Brazos River contained a variable rate, we held they were not negotiable because they did not contain an unconditional promise to pay; payment was required only if funds were available in a specified account at the time payment was due. Id. at 696. For this reason, Brazos River Authority does not control this case.
*797In support for the conclusion that “[u]se of an interest rate that cannot be calculated from information on the face of the note has consistently been held to violate the Texas statute’s ‘sum certain’ requirement,” at 801, the concurring and dissenting justices cite four cases. Two were decided by federal district courts citing no Texas state court authority.8 To the extent that federal courts have ventured an “Erie-guess” as to the applicable Texas law, and guessed differently from our answer to the present certified question, see American Waste & Pollution Control Co. v. Browning-Ferris, Inc., 949 F.2d 1384, 1386 (5th Cir.1991) (cases cited), we do not feel constrained to address those opinions except to respectfully say that we have decided this issue of unsettled Texas law differently from the way they have predicted. Finally, the two state court of appeals opinions relied upon by the concurring and dissenting justices are addressed, and disapproved, in the analysis that follows.
We note that the only two Texas state cases relied upon by the concurring and dissenting justices were both decided by the same court of appeals: Lexington Ins. Co. v. Gray, 775 S.W.2d 679 (Tex.App.—Austin 1989, writ denied) and Dillard v. NCNB Texas Nat’l Bank, 815 S.W.2d 356 (Tex.App.—Austin 1991, no writ). In Lexington the notes provided for a variable rate of interest tied to a “fluctuating ‘base rate’ established by the [b]ank.” 775 S.W.2d at 682. The court of appeals, citing only Tex.Bus. & Com.Code § 3.104(a), concluded that “the note apparently is not a negotiable instrument_” Id. This incidental holding was not determinative of the issue presented: assignability of certain guaranty agreements. Furthermore, no point of error challenging this holding of the court of appeals was brought forward to this court for review so we had no opportunity to pass on the correctness of the court of appeal’s decision.
In Dillard v. NCNB Texas Nat’l Bank, the note in question specified interest was to be paid at the lender’s prime rate plus two percent. 815 S.W.2d at 360. Summary judgment was granted in favor of the bank to which the note had been assigned and against the note’s guarantors. The note contained a written endorsement to the Federal Reserve Bank-Dallas placed on the document while in the possession of First RepublicBank. When First Republic-Bank failed, its assets, including this note, were transferred to NCNB Texas National Bank (“NCNB”) by the Federal Deposit Insurance Corporation. The issue on appeal was whether NCNB had established itself as the holder of the note as a matter of law. The court of appeals held that the note was non-negotiable and thus not subject to transfer by simple endorsement, citing Brazos River Authority and Leodngton. Id. Nevertheless, the court noted that non-negotiable instruments are assignable and that the endorsement was sufficient to raise a fact issue on whether the note had been properly assigned to the Federal Reserve Bank. Id. Because the court concluded there was a disputed fact issue as to NCNB’s status as holder of the note, it reversed the judgment in favor of NCNB and remanded the case to the trial court. Id. at 360-61. Although we consider that the issue whether VRNs are negotiable instruments is not controlled by either Dillard or Lexington in the interest of clarity we disapprove of the holdings in Dillard and Lexington to the extent they may be construed to conflict with our holding today.
Therefore, in response to the question certified to us by the United States Court of Appeals for the Fifth Circuit we reply that a promissory note requiring interest to be charged at a rate that can be determined only by reference to a bank’s published prime rate is a negotiable instrument as defined by the Texas Uniform Commercial Code. By a “bank’s published prime rate,” we intend our answer to include only those rates which are public, either known to or *798readily ascertainable by any interested person. See BLACK'S LAW DICTIONARY 1233 (6th ed. 1990). We do not, however, specify or limit the manner in which the rate must be published. The requirement of commercial certainty is satisfied when the information is readily available to the public, regardless of the means utilized to make that information available.
Having answered the certified question posed, we do not proceed to apply our answer to the facts of the case now pending before the Fifth Circuit Court of Appeals, as the concurring and dissenting justices claim to do.9 This is for two, it appears to us, obvious reasons. First, we do not have jurisdiction to decide the whole case. It would exceed this court’s constitutional and rule-based authority to apply our answer to the factual record before the Fifth Circuit. See TEX.CONST. art. V, § 3-c; TEX.R.APP.P. 114. Second, a certified question is a limited procedural device that constrains us to answer only the question certified “and nothing more.” Moreno v. Sterling Drug, Inc., 787 S.W.2d 348, 349 (Tex.1990). For these reasons, we confine our answer to the question propounded by the certifying court. How our answer is to be applied in the case before the Fifth Circuit Court of Appeals is solely the province of the certifying court.10
Concurring and dissenting opinion by DOGGETT, J., joined by MAUZY, HIGHTOWER and GAMMAGE, JJ.. All references to the Texas Uniform Commercial Code or the Code will be to the Uniform Commercial Code as enacted by the Texas Legislature and codified in the Texas Business and Commerce Code. TEX.BUS. & COM.CODE §§ 1.101-11.018.
. Section 3.106 of the Code provides:
(a) The sum payable is a sum certain even though it is to be paid
(1) with stated interest or by stated installments; or
*794(2) with stated different rates of interest before and after default or a specified date; or
(3) with a stated discount or addition if paid before or after the date fixed for payment; or
(4) with exchange or less exchange, whether at a fixed rate or at the current rate; or
(5)with costs of collection or an attorney’s fee or both upon default.
(b) Nothing in this section shall validate any term which is otherwise illegal.
TEX.BUS. & COM.CODE § 3.106.
.Arizona (ARIZ.REV.STAT.ANN. § 47-3106(B) (Supp.1991))
California (CAL.COM.CODE § 3106(2) (West Supp.1992))
Delaware (DEL.CODE ANN., tit. 6, § 3-106(l)(f) (Supp.1990))
Florida (FL.STAT.ANN. § 673.106(2) (West Supp.1991))
Indiana (IND.CODE ANN. § 26-1-3-106(1) (Michie Supp.1991))
Iowa (IOWA CODE ANN. § 554.3106(1)® (West Supp.1991))
Kentucky (KY.REV.STAT.ANN. § 355.3-106(2) (Michie/Bobbs-Merrill Supp.1991)) Louisiana (LA.REV.STAT.ANN. § 10:3-106(l)(a) (West Supp.1990))
Maryland (MD.COM.LAW CODE ANN. § 3-106(2) (Michie Supp.1991))
Mississippi (MISS.CODE ANN. § 75-3-106(2) (Supp.1991))
Missouri (MO.ANN.STAT. § 400.3-106(2) (Vernon Supp.1992))
Nevada (NEV.REV.STAT.ANN. § 104.3106(2) (Michie Supp.1991))
New York (N.Y.U.C.C.LAW § 3-106(2) (West Supp.1991))
North Dakota (N.D.CENT.CODE § 41-03-06(l)(f) (Michie Supp.1991))
Oregon (OR.REV.STAT. § 73.1060 (1989))
Tennessee (TENN.CODE ANN. §§ 47-3-104(l)(b) & 47-3-106(1)© (Michie Supp. 1991))
Virginia (VA.CODE ANN. § 8.3-106(2) '(Mi-chie Supp.1991))
Washington (WASH.REV.CODE ANN. § 62A.3-106(2) (West Supp.1991))
West Virginia (W.VA.CODE § 46-3-106(1) (Michie Supp.1991))
Reference to the legislative histories for these amendments indicate that their purpose was to eliminate confusion on this issue and codify existing commercial practice. See, e.g., First City Fed. Sav. Bank v. Bhogaonker, 715 F.Supp. 1216, 1219-20 (S.D.N.Y.1989). The bill amending section 3-106 in New York was intended "to recognize already existing commercial practices and its purpose was 'to clarify any confusion surrounding the use of variable interest rates.’ ” (citing the New York State Assembly Memorandum in Support of Legislation). Id.
. H.B. 2497 was proposed during the regular session of the 72nd Legislature. The Bill Analysis accompanying H.B. 2497 states that “H.B. 2497 is intended to clarify any confusion which may exist in this State concerning whether the common practice of using variable interest rates in promissory notes renders such notes nonnegotiable” (emphasis added). The Bill was passed by the House of Representatives on May 20, 1991 and subsequently reported to the Senate. Although the Senate Committee on Economic Development reported the bill favorably, the bill was not presented for a vote by the Senate before adjournment sine die.
. A federal district court sitting in Illinois has held VRNs to be non-negotiable, and a state court of appeals has held them to be negotiable, both while interpreting the Illinois Uniform Commercial Code. Compare Northern Trust Co. v. E.T. Clancy Export Corp., 612 F.Supp. 712, 715 (N.D.Ill.1985) with Klehm v. Grecian Chalet, Ltd., 164 Ill.App.3d 610, 115 Ill.Dec. 662, 667, 518 N.E.2d 187, 192 (1987).
. The four states that have amended their versions of the U.C.C. are Maryland, Missouri, New York and Virginia. See supra at note 3. Of those, three states amended their versions of the U.C.C. after a state court ruled that VRNs were not negotiable under then existing law. See Centerre Bank v. Campbell, 744 S.W.2d 490, 498 (Mo.App.1988); Taylor v. Roeder, 234 Va. 99, 360 S.E.2d 191, 195 (1987); A. Alport & Son, Inc. v. Hotel Evans, Inc., 65 Misc.2d 374, 317 *796N.Y.S.2d 937, 939-40 (1970). One court found VRNs to be non-negotiable under the prior version of the U.C.C. enacted by the state of Maryland after the statute had been amended to specifically provide that VRNs are negotiable. See Chemical Bank v. D3J Assocs. Ltd. Partnership, 14 U.C.C.Rep.Serv.2d (Callaghan) 790, 794, 1991 WL 58049 (D.Md.1991).
. Specifically, sub-section (a) of section 3-104 of the Uniform Commercial Code has been revised as follows:
(a) Except as provided in subsections (c) and (d), "negotiable instrument” means an unconditional promise or order to pay a fixed amount of money, with or without interest or other charges described in the promise or order, if it:
(1) is payable to bearer or to order at the time it is issued or first comes into possession of a holder;
(2) is payable on demand or at a definite time; and
(3) does not state any other undertaking or instruction by the person promising or ordering payment to do any act in addition to the payment of money, but the promise or order may contain (i) an undertaking or power to give, maintain, or protect collateral to secure payment, (ii) an authorization or power to the holder to confess judgment or realize on or dispose of collateral, or (iii) a waiver of the benefit of any law intended for the advantage or protection of an obligor.
Revised U.C.C. § 3-104(a), 2 U.L.A. 25 (1991). Section 3-112 of the UCC was then revised to define interest to specifically include VRNs. Sub-section (b) of section 3-112 provides:
(b) Interest may be stated in an instrument as a fixed or variable amount of money or it may be expressed as a fixed or variable rate or rates. The amount or rate of interest may be stated or described in the instrument in any manner and may require reference to information not contained in the instrument. If an instrument provides for interest, but the amount of interest payable cannot be ascertained from the description, interest is payable at the judgment rate in effect at the place of payment of the instrument and at the time interest first accrues.
Revised U.C.C. § 3-112(b), 2 U.L.A. 39 (1991). Under this revision, the term "sum certain” contained in section 3-104(a) as originally drafted is replaced with the term "fixed amount.” The requirement of a fixed amount applies only to principal. Revised U.C.C. § 3-112, 2 U.L.A. 39, comment 1 (1991). If the amount of interest to be paid cannot be ascertained from the description of interest contained in the instrument, interest is payable at the judgment rate. Thus, under the revisions, interest will always be determinable. Id.
. In re Gas Reclamation, Inc. Securities Litigation, 741 F.Supp. 1094 (S.D.N.Y.1990) (citing only other federal district court cases for the relevant proposition) and National Union Fire Ins. Co. v. Alexander, 728 F.Supp. 192 (S.D.N.Y.1989) (citing no Texas cases for the relevant proposition).
. Of course our rules limit consideration of a certified question from a federal appellate court to those for which "it appears that there is no controlling precedent in the decisions of the Texas Supreme Court.” TEX.R.APP.P. 114(a). Our only purpose in answering the question then is to obviate the need for the Fifth Circuit Court of Appeals to venture into "the always-dangerous undertaking of predicting what Texas courts would hold if the issue were squarely presented to them.” Stephens v. State Farm Mut. Auto. Ins. Co., 508 F.2d 1363, 1366 (5th Cir.1975). By answering certified questions for those federal appellate courts that are Erie-bound to apply Texas law, we avoid the potential that the federal courts will guess wrongly on unsettled issues, thus contributing to, rather than ameliorating confusion about the state of Texas law. We find such cooperative effort to be in the best interests of an orderly development of our own unique jurisprudence, and to the bar, as well as in the best interests of the litigants we concurrently serve.
. We do not agree with all of the concurring and dissenting justices’ observations about the certification process, and we emphatically reject any criticism, express or implied, of the United States Court of Appeals for the Fifth Circuit. We do not presume to instruct the Fifth Circuit, or any other federal court, on how they conduct their business. We specifically reject that opinion’s attribution of language to the Fifth Circuit which that court disavows.
As for the reasons why this court has conducted itself as it has in addressing certified questions, obviously, the concurring and dissenting justices’ opinion does not speak for all the justices of this Court. Caution should be observed in characterizing the actions of a collegial body on such discretionary matters. As Chief Judge Cardozo once observed, "The springs of conduct are subtle and varied.” De Cicco v. Schweizer, 221 N.Y. 431, 438, 117 N.E. 807, 810 (1917).
Texas is a comparative newcomer to the inter-jurisdictional certification process, which originated with an act of the Florida Legislature in 1945, Fla.Stat. § 25.031, and has now been adopted in some form in at least 40 states. Chief Justice Thomas R. Phillips, Certification of Questions of Law by Federal to State Courts, Presented to the Judicial Conference of the United States, Federal-State Jurisdiction Committee 1 (Jan. 16, 1992) (Manuscript on file with the Supreme Court of Texas). Texas has utilized the procedure only since the adoption of Tex. Const. art. V, § 3-c, effective January 1, 1986. The Fifth Circuit, on the other hand, has had more extensive experience with certification than any other court, state or federal. See 17A C. Wright, A. Miller & E. Cooper, Federal Practice & Procedure § 4248 at 176 (1988). Many of the practices and procedures relating to certification now in common use were first developed by that court. We acknowledge the Fifth Circuit's experience in this area and welcome constructive suggestions on how the interjurisdic-tional certification process can be improved.