In determining whether a statute of a state impairs the obligation of a contract, this court doubtless must decide for itself the existence and effect of the original contract, (although in the form of a statute,) as well as whether its obligation has been impaired. Louisville & N. R. R. v. Palmes, 109 U.S. 244, 256, 257, S.C.. 3 Sup. Ct. Rep. 193, and cases cited; Wright v. Nagle, 101 U.S. 791, 794. But the construction given by the supreme court of Louisiana to the contract relied on in the present case accords, not only with its own decision in the earlier case of Baton Rouge R. R. v. Kirkland, 33 La. Ann. 622, but with the principles often affirmed by this court.
In the leading case of Providence Bank v. Billings, 4 Pet. 514, Chief Justice MARSHALL, speaking of a partial release of the power of taxation by a state in a charter to a corporation, said: 'That the taxing power is of vital importance, that it is essential to the existence of government, are truths which it cannot be necessary to reaffirm.' 'As the whole community is interested in retaining it undiminished, that community has a right to insist that its abandonment ought not to be presumed, in a case in which the deliberate purpose of the state to abandon it does not appear.' 'We must look for the exemption in the language of the instrument; and if we do not find it there, it would be going very far to insert it by construction.' 4 Pet. 561-563. In Philadelphia & W. R. R. v. Maryland, 10 How. 376, Chief Justice TANEY said: 'This court on several occasions has held that the taxing power of a state is never presumed to be relinquished, unless the intention to relinquish is declared in clear and unambiguous terms.' 10 How. 393. In the subsequent decisions the same rule has been strictly upheld and constantly reaffirmed, in every variety of expression. It has been said that 'neither the right of taxation, nor any other power of sovereignty, will be held by this court to have been surrendered, unless such surrender is expressed in terms too plain to be mistaken;' that exemption from taxation 'should never be assumed unless the language used is too clear to admit of doubt;' that 'nothing can be taken against the state by presumption or inference; the surrender, when claimed, must be shown by clear, unambiguous language, which will admit of no reasonable construction consistent with the reservation of the power; if a doubt arise as to the intent of the legislature, that doubt must be solved in favor of the state;' that a state 'cannot by ambiguous language be deprived of this highest attribute of sovereignty;' that any contract of exemption 'is to be rigidly scrutinized, and never permitted to extend, either in scope or duration, beyond what the terms of the concession clearly require;' and that such exemptions are regarded 'as in derogation of the sovereign authority and of common right, and therefore not to be extended beyond the exact and express requirement of the grants, coustrued strictissimi juris.' Jefferson Branch Bank v. Skelly, 1 Black, 436, 446; Gilman v. Sheboygan, 2 Black, 510, 513; Delaware Railroad Tax, 18 Wall. 206, 225, 226; Hoge v. Railroad Co., 99 U.S. 348, 355; Southwestern R. R. v. Wright, 116 U.S. 231, 236; S.C.. ante, 375; Erie Ry. v. Pennsylvania, 21 Wall. 492, 499; Memphis Gas-Light Co. v. Shelby Taxing District, 109 U.S. 398, 401; S.C.. 3 Sup. Ct. Rep. 205; Tucker v. Ferguson, 22 Wall. 527, 575; West Wisconsin Ry. v. Supervisors, 93 U.S. 595, 597; Memphis & L. R. R. R. v. Railroad Com'rs, 112 U.S. 609, 617, 618; S.C.. 5 Sup. Ct. Rep. 299.