An a priori argument is one in which a fact is deduced from something which came before it. Mathematics uses this kind of reasoning – given certain prior axioms, the mathematician deduces the proof – whereas legal judgments are usually a posteriori, inferring backwards from the act to the animus.
In seeking the past through its persistence in the present, am I using one of these strategies? Memory moves both ways, for it consists of traces in the present laid down in some imagined past, and it is from these traces that we must again refer backwards, in order to evoke in the now some analogue of what happened then.
Reasoning forwards, reasoning backwards in non-existent time, we seek to approximate certainty. But as George Meredith writes in Modern Love, ‘Ah, what a dusty answer gets the soul/ When hot for certainties in this our life.’