BOND, J.
The only question presented for review is, whether defendants were guilty óf a breach of their contract with plaintiff ? If so, they must repay the discounts allowed as a part of the consideration of the agreement. Missouri E. L. & P. Co. v. Carmody, 12 Mo. App. loc. cit. 538. It is insisted for appellant that the terms of the clause under review *138were only intended to impose upon defendants the obligation to obtain all the current used in the building occupied by them at the time of the contract, from the electrical plant of the plaintiff. This contention is disproved by the express terms of the clause of the contract under review, which are to-wit: “The party of the first part (defendants) also agrees to use the service of the party of the second part exclusively, for lighting the premises herein designated, for a period of three years from the date of this instrument.” This language plainly imports an undertaking on the part of defendants, not only to buy from plaintiff, but to .continue to purchase from it for a period of three years after the formation of the contract. In consideration of these two obligations, the contract further shows that plaintiff agreed to make a remission of twenty per cent of the gross amount of its monthly bills rendered to defendants. As the defendants only performed these obligations for fourteen months, they necessarily committed a breach of their agreement to do so for three years. In the interpretation of contracts, the words used must be taken in their plain, ordinary and usual sense, and where they are free from any ambiguity or uncertainty, no room is left for construction. The language governing the obligations of defendants in its contract with plaintiff, is plain and explicit, neither have we been able to find any other expressions in the contract taken as a whole, which show that the language in question had other than its literal import when used by the parties to the instrument. The rule on this subject as stated by Mr. Greenleaf, is, to-wit: “The writing, it is true, may be read by the light of surrounding circumstances, in order more perfectly to understand the intent and meaning of the parties; but, as they have constituted the writing to be the only outward and visible expression of their meaning, no other words are to be added to it or substituted in its stead. The duty of the court in such cases is to ascertain, not *139wbat- the parties may have secretly intended, as contradistinguished from what their words express, but what is the meaning of the words they have used.” 1 Greenleaf on Evidence, sec. 277; affirmed in Koehring v. Muemminghoff, 61 Mo. loc. cit. 467; Sachleben v. Wolfe, 61 Mo. App. l. c. 35.
Our conclusion is, that the learned circuit judge attached to the contract under review the legal effect arising upon the language of the parties. His judgment is affirmed.
All concur.