What it is
Judging past decisions by information that only became available later.
In the wild
They should have acted, knowing what we know now.
How to answer it
Reconstruct what was actually known at the time of the decision.
Causal errors
Historian's fallacy
Also called Presentism in judgement
In depth
Origin and naming
Coined by historian David Hackett Fischer in his 1970 book 'Historians' Fallacies'. His target was colleagues who judged past actors as if they had read the same epilogue we have — assuming decision makers saw events from our vantage, with our information and our outcomes already known.
More places it shows up
How could the town council approve a design with that concrete? Everyone knows now it degrades — in papers published last year.
The general was incompetent; any fool could see the flank was exposed — on the satellite images we pulled decades later.
Why didn't the founders put that clause in the contract? Clause litigation only became standard practice after the case two years ago.
Judging a 1995 investor for not buying into the internet boom, based on what the internet became by 2010.
How to spot it
- The verdict rests on facts the person could not have had — dates, reports, or norms that postdate the decision.
- The critic never says when the warning information actually became available.
- Swap in what was known at the time, and the 'obvious' mistake stops being obvious.