From the Greek sophists they borrowed ingenious ways of playing off one duty against another, or duty in general against self-interest - leaving the doubter in the alternative of neglecting the one and being a knave, or neglecting the other and being a fool.
In order to lay bare the ground of certainty he raises the universal doubt, and, although, following Augustine,2 he finds its limit in the thought of the doubter, this of itself is not enough.
Thomas, who had been absent, doubts the resurrection; Jesus comes and submits to the doubter's tests.