Every sentence in order to have definite scientific meaning must be practically or at least theoretically verifiable as either true or false upon the basis of experimental measurements either practically or theoretically obtainable by carrying out a definite and previously specified operation in the future. The meaning of such a sentence is the method of its verification.

Shewhart, Walter A.; Deming, William E. (1939). Statistical Method from the Viewpoint of Quality Control. The Graduate School, The Department of Agriculture. p. 94.