delivered the opinion of the court.
In June, 1905, the Washoe Copper Company commenced an action in the district court of Silver Bow county against Michael A. Hickey and others to recover damages for trespasses upon certain real property and for an injunction to prevent the repetition of the trespasses. In its" complaint the- plaintiff *501alleges that it is the owner and entitled to the possession of lots 12, 13, and 14, of block 12, Leggat & Foster’s addition to the city of Butte, together with all the lodes, leads and minerals within each and all of said lots; that the defendants have theretofore trespassed upon the premises, extracted minerals therefrom, and threaten to continue such trespasses. In October, 1908, the defendants filed their second amended answer, in which they deny the allegations of ownership and right of possession in the plaintiff to a certain portion of the premises, which portion is described by metes and bounds. The defendants admit their entry upon the described portion and their purpose to continue operations. As an equitable counterclaim, the defendants allege that plaintiff’s claim to the premises, if any it has, is founded upon certain placer locations of the grfcgmd, by John A. Leggat and others, which locations were carried to patent, and patent received and recorded. It is then alleged that at the date of the application for placer patent there existed upon the ground a certain well known lead, lode,, or vein bearing valuable mineral, which known lead, lode or vein, together with twenty-five feet on each side, thereof, constitutes, the portion of the ground described by metes and bounds; that in the application for placer patent the locators did not apply for patent to any lead, lode or vein within the boundaries of their placer locations; that in 1903 Hickey, Lindsay and Lewis, located the ground described by metes and bounds, as the Lizzie Fraction quartz lode mining claim, and thereafter did all things' necessary to perfect their location and perpetuate the same, and thereafter made application for patent, which application was'contested by the plaintiff company, and the proceedings were1 before the land department at the time the answer was filed.. A motion was interposed to strike a part of the answer, and on February 23, 1909, sustained in an order which granted plaintiff twenty days within which to file a reply. The reply was not filed within the time allowed, and on March 30, 1909, the death of Michael A. Hickey, which occurred on January 28, 1909, was suggested to the court; Edward Hickey, special administrator of his estate, was substituted; and on motion of *502counsel for defendants the default of plaintiff, for failure to reply, was entered, and judgment for the defendants quieting their title to the land described by metes and bounds was rendered and entered. On April 2 plaintiff moved to have the default set aside, assigning as reasons, among others, inadvertence and excusable neglect. A copy of the proposed reply was tendered with the motion. On June 21, 1909, this motion came on for hearing, was heard, and disposed of in an order of the court as follows: “After argument of counsel being heard and submitted, the court grants the said motion, conditioned upon the plaintiff paying within five days all costs incurred by defendants since the filing of the second amended answer. * * * Plaintiff was by the court granted five days to reply to the second amended answer. Counsel for both parties in open court waives trial by jury, and the case was by the court set for trial on Tuesday, September 7, 1909.” At the same time, and in the presence of court and counsel for defendants, plaintiff filed its reply. On August 11, 1909, counsel for the respective parties stipulated that the setting of the cause for trial be vacated, and on August 30 the court vacated the setting pursuant to the stipulation. On April 11, 1910, defendants moved the court to dissolve all injunctions which had been issued in the cause at the instance of plaintiff; but, before this motion was heard, plaintiff moved the court for certain orders. On September 12, 1910, the court heard and denied both motions in toto. On September 19 the court filed, and .had made a part of its former order, a memorandum explanatory of its order of September 12. On September 28, 1910, plaintiff filed in court its motion to have the cause placed upon the trial calendar for trial. On October 3, the time noticed for the hearing of the last motion, defendants presented to the court their written objections to the court hearing such motion, and thereafter took no further part in the proceedings. On October 3 the court overruled defendants’ objections, granted the plaintiff’s motion, and placed the cause on the trial calendar for trial upon the pleadings theretofore filed. Counsel for defendants then presented to this court their application for a writ of prohibition. An alter*503native writ was issued, and upon the return the respondents moved to quash, and the proceeding was submitted for determination.
The principal question arises upon a construction of the order made by the trial court on June 21, 1909. That order was made upon the motion of plaintiff to set aside the judgment, open the default, and permit a reply to be filed. The order reads: “The court grants the said motion, conditioned upon plaintiff paying, within five days, all costs incurred by defendants since the filing of the second amended answer.” That the payment of costs was not intended to be a condition precedent to setting aside the default and judgment seems to us apparent: (1) The order is written in the present tense, and its effect is to set aside the judgment and open the default instanter. (2) The plaintiff was given five days within which to pay the costs. If the court intended that the payment of costs should be a condition precedent to opening the default and vacating the judgment, certainly language which more clearly expressed that intention could have been employed. (3) The amount of the costs was not specified. The judgment included five dollars costs; but the order includes all costs incurred by defendants since the filing of their second amended answer. Whether there were any costs other than the five dollars we do not know; but, in view of the language in which the order is couched, and other considerations hereafter to be noticed, it seems reasonable that the court intended that some claim for costs should be presented by the defendants who were in a position to know what costs they had incurred between the dates mentioned. (4) The court in effect construed its order as one operating in prcesenti: (a) As a part of the same order, the court granted the plaintiff five days within which to file its reply. If the default and judgment were not set aside, the plaintiff had no right to file a reply, and it is only upon the theory that the order was intended to act in prce-senti that there can be any justification whatever for the action of the court in granting leave to reply. Under this latter provision of the order, the reply might have been filed on the same day and immediately upon leave being granted—which *504was the fact in this instance—although the costs need not have been paid until the last hour of the fifth day thereafter, (b) The court at the time set the cause for trial. If the default and judgment had not been set aside, there was not any cause to be tried, and this part of the court’s order would be ridiculous. It is only upon the theory that the order setting aside the judgment and default operated in prcesenti that there can be any possible justification for this portion of the order. (5) Counsel for both parties also gave a like construction to the order. The minutes recite that, upon the order being made setting aside the default and judgment, “counsel for both parties in open court waived trial by jury.” Waived trial of what? If the judgment and default had not been set aside, there was not anything to be tried, and the fact that counsel for defendants waived a jury trial is inexplicable upon any theory except that they understood the order to operate in the present.
If we were compelled to construe the order setting aside the default as if it stood alone, we might experience some difficulty. The courts have not agreed as to the meaning of such orders. In each of the following cases, it was held that the payment of the amount mentioned was a condition precedent to the order taking effect: Gregory v. Haynes, 21 Cal. 443; Hartman v. Olvera, 49 Cal. 101; Sands v. M’Clelan, 6 Cow. (N. Y.) 582; Friese v. Homeopathic M. L. Ins. Co., 107 Pa. 134; Mabley v. Superior Court, 41 Mich. 31, 1 N. W. 985. On the contrary, in Dana v. Gill, 5 J. J. Marsh. (Ky.) 242, 20 Am. Dec. 255, the order read: “It is ordered that the nonsuit rendered herein be set aside, upon payment of costs.” The court said: “What effect, then, shall that part of the order have, which declares the nonsuit to be set aside, upon payment of costs? We answer: No other than to impose an obligation upon the plaintiff to pay the costs occasioned by his default, and, if he does not, it may furnish a good cause for attachment, to compel their payment or justify suing out execution for the amount. * * * Our construction of the order setting aside the nonsuit in this ease is that it is positive, and not contingent; and the language is that *505usually employed by clerks to show that the nonsuit was set aside, and that the plaintiff should pay the costs. ’ ’
In Gilliland v. Rappleyea, 15 N. J. L. 138, the order was: “That the verdict be set aside and a new trial granted on payment of costs.” The court said: “But the payment of costs, when it is ordered, is annexed as a condition upon which the party may have a new trial, and yet not strictly as a condition in such a sense that, if it is not performed, there shall be no new trial. It is rather an order on the party at whose instance the verdict has been set aside that he shall pay the costs of the first trial, which order, like other interlocutory orders, may be enforced by attachment.”
In People ex rel. Attorney General v. Murphy, 119 Ill. 159, 6 N. E. 488, the court said: “It is a familiar rule of construction that when the terms of an agreement are in any respect doubtful or uncertain, and the parties to it have, by their own conduct, placed a construction upon it which is reasonable, such construction will be adopted by the courts, in the event of litigation concerning it.” This rule may very well be said to be one of universal recognition. While it applies primarily to contracts and like instruments, we do not see any reason for its application to them which is not equally cogent for its application to an order of court. In fact, the supreme court of the United States appears to have laid great stress upon the theory of an order of court entertained and acted upon by the litigating parties in Ex parte Ransom v. City of New York, 20 How. 581, 15 L. Ed. 1000, where, in discussing a ease somewhat similar to the one before us, in the course of the opinion it said: “We concur in this view of the court, and we are also satisfied, from the course of the proceedings preparatory to the motion for the new trial, the hearing of that motion, and' the turning of the case into a bill of exceptions with a view to a writ of error, it was the understanding of both parties that the judgment of the 12th of December was to be considered as vacated.”
It has been the rule in this state for many years that: “When a cause has been tried upon a certain well-defined theory, neither party will be heard in this court, on oral argument, for the first *506time to assume a position antagonistic to such theory.” (Talbott v. Butte City Water Co., 29 Mont. 17, 73 Pac. 1111.) The rule announced in People v. Murphy and recognized by the supreme court of the United States is known as the rule of practical or contemporaneous construction, and the reason for its application is the same as that for the rule announced in the Talbott Case, viz.: That a party will not be heard to shift his position to the prejudice of his adversary. The fact that counsel for defendants acted upon the order of June 21, 1909, as though it operated to set aside the judgment at that time, may well have led the plaintiff to believe that a memorandum of costs would be presented, and, until presented, the costs were not to be paid; or that the costs should be paid within five days if the cost bill was presented within that time. To hold that the payment of costs was a condition precedent to the order taking effect would do violence to the construction placed upon the order by the trial court and counsel for both parties, and would have the effect of denying a trial of the cause upon the merits; while to hold the contrary carries out the manifest understanding of the lower court and counsel and insures a trial upon the merits—a result which ought to be accomplished in every case if it can be without prejudice to any substantial right of either party. If there was not any other reason for our conclusion, we would not hesitate to declare this sufficient. There is, however, another consideration which seems to justify the same result.
The plaintiff was defaulted by reason of its failure to file a reply within twenty days after February 23, 1909. When the order fixing that time was made, Michael A. Hickey, one of the defendants and a necessary party, had died. The authority of the attorneys for defendants to represent him ceased until there was a substitution of his administrator, which was not made until March 30. From the date of his (Hickey’s) death on January 28, until the substitution was made, there was not anyone upon whom service of a reply could be made so far as that defendant’s interest was concerned. Under such circumstances, plaintiff was entitled to a reasonable time at least, after the substitution was made, to serve and file the reply; but there was *507not any time allowed whatever, and the judgment of March 30, so far as it affected the estate of Michael A. Hickey, was entered prematurely and was a nullity. In Palmer v. McMaster, 8 Mont. 186, 19 Pac. 585, this court said: “A judgment by default entered too soon is as much a nullity as if it had been taken on a defective service.” If, then, the default should not have been entered in the first instance, it should have been set aside without condition.
Upon the entire record as presented, we think the trial court had, and now has, jurisdiction to try the cause upon the merits, and its further proceeding will not be restrained. The motion to quash is sustained, and the proceeding is dismissed.
Dismissed.
Mr. Chief Justice Brantly and Mr. Justice Smith concur.