Circumstantial evidence requires a deduction, a leading away from what is obvious, from what appears on the surface, towards a truth. It begins with evidence, continues with an act of imagination and insight and then traces its way back to origins known, retrospectively making sense of both the circumstances and the conclusion in one movement of return.
A person discovering a river immediately stands there and judges the flow, the water's shape and direction. This leads to the sea, he claims, although he cannot see the sea himself.
He gathers evidence, citing the foliage on the banks, the silver slip of fish upstream. He climbs hills looking for the source, all the time following the river as it reduces to a trickle. The hills, the shape, the flow, the willows and fish. This is a river and it leads to the sea, he infers. Braced now with enough evidence, he walks for many days and nights along the river's edge until arriving at the river's mouth, a vast estuary, and beyond that, the salty sea.
At that moment, the evidence of the river proves that the sea is in fact a sea, it is a large body of saline water into which one or more rivers flow.
Simultaneously, the sea proves the river – it is not a canal, or a long lake or any other body of water. It has a source and empties itself into a sea. At that moment, the sea is the sea, the river is a river, indeed the fish are fish, the edges of earth are banks and the glinting stones are part of that river's bed.