MoCLELLAN, J.
Prior to March 18, 1912, Misses Dickert and Landt (appellees) owned and operated the Anniston Hospital, and Drs. E. M. and W. D. Sellers (appellants) owned and operated the Sellers Hospital. With the purpose of establishing out of these two prop*211erties, and equipments, and institutions a public hospital in Anniston, Misses Dickert and Landt constituted Drs. Winn and Moore their agents to negotiate with the Drs. Sellers, and also bind them in the premises. On March 18, 1912, the Drs. Sellers and Misses Dickert and Landt (through the hand of one of their agents) signed the instrument of which the following is the substance: “Know all men by these presents that this contract is hereby made by and between M. O. Dickert and O. Y. Landt, doing business as the Anniston Hospital Company, party of the first part, and E. M. Sellers and W. D. Sellers, party of the second part, and it is mutually agreed and understood as follows: That, in consideration of the mutual agreement of the parties hereto, the parties of the first part contract and agree to sell and convey to the said parties of the second part the equipment, and outfit, and all property connected therewith, not including the real estate in which the same is located, of the said Anniston Hospital Company in consideration of the sum of one ($1.00) dollar to be paid by the said parties of the second part to- the parties of the-first part; and the parties of the second part contract and agree, upon receipt of the said conveyance of the-equipment of the Anniston Hospital Company; to sell and convey by good and sufficient deeds, with covenants-of warranty, the property known as the Sellers Hospital, and all equipment connected therewith,' and also-the property which shall have been conveyed to the parties of the second part by said Dickert and Lándt, and which is above referred to, to certain named trustees to be agreed upon for the benefit of the public, at and for-the consideration to be paid to- the parties of the second part of the sum of twenty-five thousand ($25,000.00) dollars, said payment to be made as follows: The sum of five thousand ($5,000.00) dollars in sixty days, and *212the balance of said purchase money in five annual installments of four thousand ($4,000.00) dollars each, with interest on each note payable annually at eight per cent, per annum.”
On March 30, 1912, the Drs. Sellers executed the instrument, called a duebill in the record, in words and figures as follows: “Due Drs. Moore and L. M. Winn $1,000 in 60 days, provided by the terms of the original contract.” This is the foundation of the present suit; common counts and counts in special assumpsit being employed in the statement of the cause of action. While mere mention is made in brief for appellant that the court erred, as assigned, in overruling the demurrer to count 2 as amended, no insistence upon this assignment appears in the brief for appellant. There is no assignment of error insisted upon that is predicated of rulings on the pleadings.
The major question presented for review is the propriety of the trial court’s action in allowing the plaintiff to adduce evidence of obligations assumed or promises made outside of the instrument of March 18, 1912, quoted above. The real issue between parties may be made to more clearly appear by stating, summarily, the respective concrete contentions: For the plaintiffs, that defendants engaged to pay plaintiffs, in any event, $2,-000 for their-unqualified contribution, in property, to the unit made by the aggregation of both the hospital properties, which, it was the expectation and purpose, would, in effect, be sold to the public, represented by trustees, and paid for, to the defendants as the temporary repositories of the title, by popular subscription, and the other $1,000 was represented by the duebill, made payable to the mentioned agents of the plaintiffs, who were without pecuniary interest therein; and, for the defendants, that there was no assumption by them *213of an absolute obligation to pay plaintiffs $2,000, but only to pay them that sum if the sum to be raised in a definite time by popular subscription was paid to the defendants — a condition that was not met— the scheme being to sell the combined property to trustees for the public for $25,000, $2,000 of which should go to- the plaintiffs for their property contribution, and the rest to defendants, and that the duebill was but a token of the balance ($1,000 having already been paid by defendants), to pay which the assurance was wholly contingent upon the event stated. It is thus seen that the paramount substantial issue was whether the defendants engaged unqualifiedly to pay $2,000 to plaintiffs for their hospital property. If the defendants’ theory of the matter was sustained, of course the plaintiffs could not recover; but, if that of the plaintiffs prevailed, the liability of defendants was established. In the process of supporting their theory the court allow the plaintiffs, over the defendants’ objections, to introduce parol evidence dehors the writing of March 18, 1912. This testimony was to the effect that a contract consistent with the plaintiffs’ theory, stated before, was made, and that the duebill was an accordant element thereof —a contract not fully set forth in the writing of March 18, 1912. The basis of the objections made 'for defendants was the familiar doctrine which forbids the adduction of parol evidence to vary, alter, or contradict a written contract; and it is earnestly insisted for appellants that the matters of evidence admitted for plaintiffs do not fall within any of the recognized “exceptions” to the general doctrine mentioned. Counsel say, in substance in this connection, that the application of the law, and not the law, is the real subject of their controversy.
The general doctrine invoked for appellants necessarily rests upon the existence of a valid written in*214strument expressing the obligations assumed by or imposed upon the parties. The implication, at least, is that the executed writing contains all stipulations, engagements, and promises the parties intend to make or to assume, and that all previous negotiations,, conversations, and parol agreements are merged in the terms of the instrument.
The basis for this action — the bill of sale quoted before — was executed 12 days after March 18, 1912, and at least that number of days after the parol agreements to which the witnesses were allowed to testify. In effect the first clause of the duebill said: “I owe Doctors Moore and Winn one thousand dollars, to be paid in sixty days from March 30, 1912.” To this there is added, “provided by the terms of the original contract.” Manifestly, the express reference there made to an “original contract” required parol evidence to identify the subject of the reference. The duebill did not describe the “original contract,” either by date or other expressly identifying method. If it had definitely referred to the instrument of March 18, 1912, then there would be presented the unalloyed question to which counsel have devoted an able and elaborate discussion. The paper not having done so, it is clear that parol evidence was properly receivable to identify the “original contract.” But evidence to identify a contract referred to in another paper and evidence to alter, vary, or contradict, if so, a written contract referred to in another paper, which has been identified, are, of course, very different matters — matters not to be confounded when due regard for established rules of evidence is required.
Under this duebill, a vitally important inquiry of fact was, What were the “terms of the original contract”? There was no possible way in which to estab*215lish the fact other than by evidence aliunde the due-bill. The instrument of March 18, 1912, itself did not establish the fact, though it was undoubtedly evidence tending so to do when parol evidence was presented to evidentially refer the terms of the duebill to that instrument. The defendants, in effect, affirm that the reference in the duebill was to the instrument of March 18, 1912, and to nothing else; but the plaintiffs contested that affirmation, and asserted through their testimony that that instrument was not alone the “original contract” — that the “original contract” had another feature which supported the liability the duebill evidenced. Hence, before the doctrine appellants would invoice could have operation and effect, it would be necessary to affirm, as a matter of law, that the written instrument toas the “original contract” referred to in the duebill. Obviously, this could not be done by the trial court without deciding an issue which was necessarily a question for the jury.
In determining what was the “original contract,” those advantaged to know the facts were the sources of information in the premises, and it was competent to ask them in the words of the duebill, or in other equivalent phrases, what were “the terms of the original contract,” and thereby offend no rule forbidding the interpretation or construction of written instruments by other than the court itself. Such questions evoke knowledge of a fact or a combination of facts comprehended in the term “contract.” The several assignments of error grouped as A under subdivision 3 of appellants’ brief are without merit.
There was manifest error in allowing, over defendants’ apt objection, the question, copied in assignment 23, propounded to the witness Dr. Moore whereby the witness was asked to interpret the reference in the due-*216bill. It is ever the function of the court, and never the privilege of a witness, to construe or interpret a writing in evidence. The motion to exclude the answer to this- question was also erroneously overruled. The question set out in assignment 26 was subject to- like fault, and it was error to allow it over defendants’ objection.
There was error, also, in permitting the witness Winn to testify that the duebill was given for the balance of the purchase money. Whether it was given therefor or not depended upon what “the terms of the original contract” were. It was competent for the witness to testify what those terms were — what the original contract was — but for the jury to determine the issue what the “original contract” was. To allow the witness to testify to the effect indicated was to permit him to affirm that which, under the evidence, only the jury could decide.
For the errors indicated, the judgment is reversed, and the cause is remanded.
Reversed and remanded.
Mayfield, Sayre, and Somerville, JJ., concur.