If you are told or otherwise believe an either—or proposition, the question may easily arise what makes it true. ‘The potato crop in Ruritania was halved by blight in 1928’ — ‘Well then, either the expected, planned-for crop was in excess of the people's needs, or there was a shortage of potatoes that year, or a lot were imported …’. That seems a fair deduction, and we may ask which was true. If only one was, then we'd say it made the disjunction true. If all were, then all of them did.