a romantic view of causal inference

In Mary Shelley’s 1818 novel Frankenstein; or, The modern Prometheus, the title character, scientist Victor Frankenstein, is trying to solve a mystery when an idea occurs to him, and we come across this fabulous line.

“I could not doubt it. The mere presence of the idea was an irresistible proof of the fact.”

My papers would be a lot shorter (and a lot of them are already short) if I could rely on “proof by idea.” In an authorial twist, Leslie Klinger’s annotated edition claims that these sentences were added by Percy Shelley to Mary Shelley’s draft, lest you feel tempted to hold Ms. Shelley responsible for these unidentified claims.