The contract of March 6, 1909, provided that
“Final cash settlement hereunder shall become due and shall be paid on demand after such expiration of time, but only on the conditions, viz.,
“1. That no lien, attachment, or incumbrance caused or suffered by the contractors then lawfully exist in the premises, and
“2. That the owners be then restrained from making such payment by no legal process; and
“ 3. That at such time the final balance on all accounts then due the contractors from the owners in the premises shall have been found and certified accordingly in writing by the architects and the contractors, or found and determined by the award of the arbitrators as hereinafter provided. ”
It is the defendants’ contention that the payment of the $10,000 specified in the agreement of compromise of February 15, 1911, was made subject to the third clause set forth above as well *192as to the first and second clauses by virtue of the provision in the agreement of compromise that “The balance [$10,000, was] to be paid as provided by the terms of said contract. ” That is to say, the $10,000 was to be paid when the architects certified that the work was “ complete and perfect in every respect . . . to the satisfaction of Winslow, Bigelow & Wadsworth, successors to Winslow & Bigelow, of Boston, Architects. ” If this be the true meaning of that clause, the controversy which was settled by the agreement of compromise was a controversy as to the amount due or to become due, not a controversy as to the amount then due.
It is the plaintiff’s contention on the other hand that the controversy which was settled by the agreement of compromise was as to the amount then due and that consequently compliance with the third clause set forth above was dispensed with by the agreement of compromise which fixed the amount then due. That left the first and second clauses as the only provisions of the original contract on which the words in question (namely, “The balance to be paid as provided by the terms of said contract”) should operate. In that case the balance was to be paid at the time provided by the contract, not as provided by all the terms of said contract.
A controversy as to the amount due does not ordinarily arise between a contractor and the owner until the contractor asserts that he has completed his work, and, if a controversy as to the amount due arises when a contractor asserts that he has completed his work, the controversy as to the amount due includes inter alla the question whether the work has been completed. For these reasons, in the absence of evidence as to the circumstances under which the contract was made, we are of opinion that the construction given to the agreement in the Superior Court was correct.
But we are also of opinion that the wording of the contract is not plain, and that evidence of the circumstances under which it was made is admissible to ascertain the true meaning of it.
Formerly the rule on which the courts went in admitting or excluding such evidence was Lord Bacon’s distinction between a patent and a latent ambiguity. See for example Putnam v. Bond, 100 Mass. 58. As to Lord Bacon’s distinction see Wig-*193more, Ev. §§ 2472 et seq. But in the later cases, if the wording of the contract is such that the circumstances under which it was made would control the meaning to be given to it, the evidence has been admitted. See for example Proctor v. Hartigan, 143 Mass. 462; Macdonald v. Dana, 154 Mass. 152; Bassett v. Rogers, 162 Mass. 47. The reason why it is not competent to add to, contradict or vary a written agreement is because where a trade between two parties is struck by their entering into an agreement in writing the trade struck is that stated in the written agreement. Butterick Publishing Co. v. Fisher, 203 Mass. 122. If the terms of the trade which are in writing are plain, they cannot be added to, contradicted or varied by paroi. But if they are not plain, the true meaning of them can be ascertained by evidence of the circumstances under which the written contract was made.
In the case at bar the defendant offered to prove “that it was the purpose of the parties to provide that the $10,000 should be paid only when the waterproofing of the sub-basement was completed in accordance with the terms of the contract. ” That was in effect an offer to prove that at the date of the contract there was no controversy as to the fact that the contract had not been completed by reason of the failure to finish the waterproofing of the sub-basement. If there was in fact no controversy in respect to the contract not having been completed, this agreement could not be construed to be a settlement of a controversy as to that matter and the construction contended for by the defendants must be adopted.
Exceptions sustained.