Tweedledum said to Tweedledee

Part of a series which began with Fake news and the ethics of belief.


I believe you should only believe something on the basis of evidence!


Interesting. So what evidence do you base that belief on?

Tweedledum and Tweedledee Tenniel

Last time we introduced William Clifford’s evidence principle:

…it is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence.

For convenience we’ll call this  ‘CP’ (for ‘Clifford’s Principle’).

We also said we should look at two main types of belief in relation to CP: descriptive beliefs and prescriptive beliefs. Here are a few examples:

Descriptive beliefs

Prescriptive beliefs

  • I was born after the Second World War
  • Water is a compound of hydrogen and oxygen
  • Global temperatures are rising as a result of human activity
  • There is a God
  • God wants me to fly this plane into the World Trade Center
  • I ought to do more exercise
  • You should watch your language
  • We ought to believe in God
  • I should do what God tells me to do
  • I ought to fly this plane into the World Trade Center
  • You should only believe something on the basis of evidence

The exchange between Tweedledum and Tweedledee could make us think a principle like CP is a non-starter. If we can’t believe CP unless we have sufficient evidence for it then we shouldn’t start applying it – even to itself.

But before we throw the baby out with the bathwater, what about restricting the principle just to descriptive beliefs? So instead of CP as Clifford worded it, we’ll try:

It is wrong to believe anything, within the category of descriptive belief, on insufficient evidence.

We’ll call this ‘EP1’ – short for ‘Evidence Principle – Take 1’.

This may not turn out to be too much of a limitation because, as I hope we’ll eventually discover, it might be hard to see what would actually count as evidence for a prescriptive belief.

Read on.

© Chris Lawrence 2021

8 thoughts on “Tweedledum said to Tweedledee

  1. Pingback: What is and what ought to be | some strong language

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