Circumstantial evidence is evidence.
Circumstantial evidence is a very tricky thing. It may seem to point very straight to one thing, but if you shift your own point of view a little, you may find it pointing in an equally uncompromising manner to something entirely different.
It is always good to know which ideas cannot be checked directly, but it is not necessary to remove them all. It is not true that we can pursue science completely by using only those concepts which are directly subject to experiment.
Circumstantial evidence … that wonderful fabric which is built out of straws collected at every point of the compass, and which is yet strong enough to hang a man.
See {630401} for a similar quotation.
Circumstantial evidence is occasionally very convincing, as when you find a trout in the milk, to quote Thoreau's example.
Results rarely specify their causes unambiguously. If we have no direct evidence of fossils or human chronicles, if we are forced to infer a process only from its modern results, then we are usually stymied or reduced to speculation about probabilities. For many roads lead to almost any Rome.
The atom can't be seen, yet its existence can be proved. And it is simple to prove that it can't ever be seen. It has to be studied by indirect evidence - and the technical difficulty has been compared to asking a man who has never seen a piano to describe a piano from the sound it would make falling downstairs in the dark.
An idea is like a rare bird which cannot be seen. What one sees is the trembling of the branch it has just left.
