Chisholm imagines that Adam and Noah exist here in the actual world, w1, and that each of them has his own collection of properties. He assumes (following Genesis 5) that Adam actually lives to the age of 930 years, whereas Noah lives to the age of 950 years. Chisholm asks us to imagine a nearby possible world in which Adam lives one more year, dying at age 931 instead of 930, and in which Noah lives one year less, dying at age 949 instead of 950. By imagining further similar one year alterations in life-span, we finally reach a possible world in which Adam lives to the age of 950 and Noah lives to the age of 930. Thus, in that world Adam and Noah have “swapped ages”. In that world Adam has the age that Noah has in w1, and Noah has the age that Adam has in w1.