concurring in the remand.
While I agree with much of the majority opinion, and agree that a remand is in order, I fear the Court may have unnecessarily complicated the standard by which the jurisdictional question on remand is to be governed. I therefore write separately to express my concern on this issue.
As stated by the majority, if the Spaeths’ land is “trust or restricted Indian land,” their suit is barred by section 2409a and we lack subject matter jurisdiction. See United States v. Sherwood, 312 U.S. 584, 61 S.Ct. 767, 85 L.Ed. 1058 (1941) (defense of sovereign immunity is jurisdictional).1 I agree that because the present record is inadequate to resolve several key legal and factual issues, a remand is required for the district court to make findings of fact and conclusions of law on these issues. However, I cannot subscribe to the use of a “substantial possibility” standard. To me, this is simply a situation where the threshold jurisdictional issue is intertwined with the merits and must be decided. Either we have jurisdiction or we do not! If in deciding jurisdiction we also decide the merits, so be it.
It is established that a court has jurisdiction to determine whether it has jurisdiction. Wright, Miller & Cooper, Federal Practice and Procedure: Jurisdiction 2d § 3536 (1984). As a corollary to this rule, “if the attack on jurisdiction requires the court to consider the merits of the case, the court has jurisdiction to proceed to a decision on the merits.” Thornhill Publishing Co. v. General Telephone & Electronics, 594 F.2d 730, 734 (9th Cir.1979); see Land v. Dollar, 330 U.S. 731, 739, 67 S.Ct. 1009, 1013, 91 L.Ed. 1209 (1947); Eastern Kentucky Welfare Rights Org. v. Simon, 506 F.2d 1278, 1283 (D.C.Cir.1974), vacated on other grounds, 426 U.S. 26, 96 S.Ct. 1917, 48 L.Ed.2d 450 (1976).
The only logical way to ascertain whether the Spaeths’ land is correctly categorized as “trust or restricted Indian land” within the meaning of section 2409a, and hence whether there is federal subject matter jurisdiction, is to determine whether the solicitor’s 1979 Opinion was correct in extending Zay Zah beyond the tax forfeiture situation. For it is only if it was so correctly extended that the Spaeths’ property could properly be considered restricted by federal law within the meaning of section 2409a. If Zay Zah was not correctly extended by the Solicitor, the Spaeths’ land could not rationally be considered “trust or restricted Indian land.”
I would therefore remand the case for the district court to make findings and con*948elusions after the following issues have been fully briefed by the parties: (1) whether the Solicitor was correct in extending Zay Zah to estates of mixed-blood Indians which had been probated in state court and not by the Secretary of the Interior and in extending Zay Zah to land transfers by female mixed-blood Indians aged eighteen to twenty years old; (2) if the Solicitor correctly extended Zay Zah to these situations, it should determine whether the Solicitor’s 1979 Opinion should be applied retroactively; and (3) if the Solicitor’s 1979 Opinion is correct and should be applied retroactively, the district court should make a factual determination as to whether reprobating the land under federal law will actually adversely affect the Spaeths’ title, and, if so, how much of their land will be so affected. These are essentially the questions outlined by the majority opinion but without the inclusion of the “substantial possibility” standard.
Only by resolving the above issues can the court determine if the Spaeths’ land is, as a matter of law and fact, “trust or restricted Indian land.” United States v. Phillips, 362 F.Supp. 462 (D.Neb.1973). If it is, then dismissal of the Spaeths’ suit would be for lack of jurisdiction. If it is not, judgment could be entered for the Spaeths on the merits. Because these issues must be addressed regardless of whether one denominates them jurisdictional or whether one considers them to be decisions on the merits, I would not inject additional considerations into the already difficult analysis. In short, I would decide the question whether we have jurisdiction, not the question whether there is a “substantial possibility” that we have jurisdiction.2 However, because I agree that a remand is necessary for the district court to address the issues which have been outlined after they have been fully briefed by the parties, I concur in the remand.
. While 28 U.S.C. § 1346(f) confers jurisdiction on federal district courts for actions under section 2409a, Wright, Miller & Cooper, Federal Practice and Procedure: Jurisdiction § 3656 (1976), section 2409a itself may deprive the court of jurisdiction.
. Lest it be said that the merits should not be decided "behind the back" of the government, see Louisiana v. Garfield, 211 U.S. 70, 78, 29 S.Ct. 31, 33, 53 L.Ed. 92 (1908), it may be noted that the United States and its representatives are in the lawsuit now. They are entitled to a decision and doubtless will fully participate in the proceedings on remand.