Lesson · 4 min Gentle
How Much Should This Move Me?
In one line A fact counts as evidence by how much more expected it is if the claim is true than if it is false.
A fact supports a claim only if it is more likely when the claim is true than when it is false. That ratio is its strength. A fever is some evidence of flu, but fevers come with many illnesses, so it is weak. A test positive in most flu cases and in few others is strong.
So ask two questions, not one. How expected is this if the claim is true? How expected is it if the claim is false? A detail that fits the story feels like proof even when it would be just as common if the story were false.
Hume weighed reports of miracles the same way: believe one only if its being false would be more surprising than the event. Strong evidence raises a claim; it does not settle it. How likely the claim was to begin with is the other half.
The late reply
Imani texts a friend about a loan and hears nothing for a day. She takes the silence as a sign that he is avoiding her. Her sister asks two questions. If he were avoiding her, how likely is a day’s silence? Quite likely. If he were not, how likely? Also quite likely: he answers slowly at the best of times.
The fact fits both stories almost equally, so it should barely move her. A reply that dodged the question would be far more telling.
Try this today Take one piece of news that convinced you today and ask how expected it would be if the claim were false; then say how much it should move you.
Cite or share this lesson
A plain reference you can paste into notes or an essay:
Quest2Reason. “How Much Should This Move Me?.” https://quest2reason.com/learn/lesson/how-much-should-it-move-me. Accessed 13 November 2026.
Sources
- Stanford Encyclopedia of Philosophy, “Bayes’ Theorem” — Defines the likelihood of a claim and the likelihood ratio, how much better a claim predicts the evidence than its denial does.
- Stanford Encyclopedia of Philosophy, “Confirmation” — Section 3 on Bayesian confirmation: what makes a fact count for or against a claim, and the likelihood ratio as a measure.
- David Hume, An Enquiry Concerning Human Understanding — Section X, “Of Miracles”: weigh a report against the chance that the report itself is false.