Opinion by
Head, J.,
It was not the purpose of the plaintiff, in filing this bill, to invoke the general jurisdiction of a court of equity to try and determine his controversy with the defendant. For that purpose he had sought the aid of a court of law and begun his action therein. From this, however, it does not follow that he may not properly go into a court of equity in an ancillary proceeding, the object of which is to aid the law court in the disposition of the action therein pending. Indeed, such is the very nature of a bill for discovery, as will clearly appear from the following definition of such a bill selected from the many contained in the various text-books on the subject: “A bill of discovery was a bill which asked no relief but simply the discovery of facts resting in the knowledge of the defendant, or of deeds or writings in the possession or the power of the defendant, in order to maintain the right or title of *443the party asking it, in some suit or action or other proceeding in another court:” Eaton on Equity, p. 630.
*444Nor has this ancient remedy been displaced because our common-law courts have power, under the act of February 27,1798, 3 Sm. Laws, 303, to compel by rule the production on the trial of books, papers, documents, etc. The present case may fairly illustrate why this should not be so. The alleged facts in the possession of the defendant which the plaintiff seeks to discover in this proceeding are necessary, not merely to aid him by way of proof at the trial, but also to enable him, by proper averment, to so prepare his pleadings that the desired evidence would be admissible on the trial, and not subject to objections that might be raised for want of proper notice in the pleadings and the like. If the plaintiff, in a case like the present cannot, by this proceeding, have discovery of the facts which he alleges make out his claim, and could only first obtain such knowledge at the trial, he would probably be driven to an amendment of his pleadings, and the trial of his cause would thus be attended with that useless expense and delay so naturally irritating to litigants in our courts. It has been pointed out by Mr. Justice Mitchell in Dock v. Dock, 180 Pa. 14" court="Pa." date_filed="1897-01-25" href="https://app.midpage.ai/document/dock-v-dock-6244127?utm_source=webapp" opinion_id="6244127">180 Pa. 14,; that the remedy afforded by the act of 1798 to a party litigant in an action at law is often entirely inadequate, and therefore ought not to conclude him from availing himself of a better remedy: “The remedy at law is neither convenient nor adequate. The bill is first for discovery in aid of a defense to the suit. Under the act of 1798 the appellant might have had a rule to produce at the trial such letters and alleged copies as appellant could specify :'with reasonable precision beforehand, but the bill avers *445that she had in fact written no such letters as appellee charged, and the contents of the alleged copies were therefore entirely unknown to her.”
*443Of course if it should appear on the face of such a bill that the claim or defense, in aid of which discovery was sought, could not be maintained because forbidden by law or contrary to public policy, or for other such conclusive reason, the bill would be demurrable and discovery would be refused. But if the bill exhibit a proper case for discovery, the defendant therein cannot, by his answer, require proof of the main fact in controversy between the parties as an essential preliminary to the discovery sought. Were it otherwise, the limited jurisdiction invoked by the plaintiff in the bill would be at once extended so as to require of a court of equity, in a purely ancillary proceeding, the determination of the main question involved, and thus the judgment of the law court, in which the action had been begun, would be forestalled. Thus it is said in Beach on Modern Equity Jurisprudence, sec. 857: “The defendant cannot defeat a discovery by denying that the evidence will be of assistance to complainant. It is only where it can be seen that the interrogatories, if answered affirmatively, would not assist the plaintiff, that they will be dispensed with; and if the party of whom discovery is sought answer at all, he must answer freely: he cannot deny the truth of the principal fact, upon which plaintiff’s right to discovery is based, and decline answering as to matters which would tend to prove the fact so denied.” In Bains v. Goldey, 35 Pa. 51" court="Pa." date_filed="1860-07-01" href="https://app.midpage.ai/document/bains-v-goldey-6231058?utm_source=webapp" opinion_id="6231058">35 Pa. 51, the following syllabus fairly indicates the view of such a proceeding taken by Judge Sharswood and adopted by the Supreme Court: “Under the 39th rule in equity, it is not competent for the defendant in a bill of discovery, in aid of an issue at law, to deny the truth of the principal fact upon which is based the plaintiff’s right to recover, and to decline answering as to matters which would tend to prove the truth of the fact so denied; he must make discovery as to all matters which tend to prove the plaintiff’s case in the issue at law.” From the opinion of that eminent jurist in the same case *444we clearly observe the true guiding principle in such cases: “Discovery in aid of a suit or defense at law is much favored in equity. It is important to the just determination of issues, that all material facts should be submitted to the consideration of the tribunal which is ultimately to pass upon the case. Where a party appeals to the conscience of his opponent, to discover facts lying in his own knowledge, it must be some strong equity or stringent rule of policy, that should form a bar to the discovery.”
*445It appears to us therefore that the plaintiff in his bill has presented a proper case for discovery, and the record discloses no satisfactory reason why he should not have it. The decree entered by the learned court below carefully guards against any unnecessary injury to the defendant by the publication of the records of his business, and leaves the defendant no just ground for complaint. The assignments of error are therefore overruled.
Decree affirmed.