The weight of evidence for an extraordinary claim must be proportioned to its strangeness.
Interpretation
Extraordinary claims require substantial evidence to be accepted.
This quote by Pierre-Simon Laplace highlights the principle that the more unusual or extraordinary a claim is, the stronger the evidence must be to support it. It emphasizes a critical thinking approach to evaluating assertions, especially in scientific and rational discourse.
In practice
In a debate about the existence of aliens, one might use this quote to emphasize the need for solid evidence.
Without any doubt, the regularity which astronomy shows us in the movements of the comets takes place in all phenomena. The trajectory of a simple molecule of air or vapour is regulated in a manner as certain as that of the planetary orbits; the only difference between them is that which is contributed by our ignorance. Probability is relative in part to this ignorance, and in part to our knowledge.
It is interesting thus to follow the intellectual truths of analysis in the phenomena of nature. This correspondence, of which the system of the world will offer us numerous examples, makes one of the greatest charms attached to mathematical speculations.
All the effects of Nature are only the mathematical consequences of a small number of immutable laws.
The word 'chance' then expresses only our ignorance of the causes of the phenomena that we observe to occur and to succeed one another in no apparent order. Probability is relative in part to this ignorance, and in part to our knowledge.
Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective positions of the beings which compose it, if moreover this intelligence were vast enough to submit these data to analysis, it would embrace in the same formula both the movements of the largest bodies in the universe and those of the lightest atom; to it nothing would be uncertain, and the future as the past would be present to its eye.
Probability theory is nothing but common sense reduced to calculation.
From the growth of the Internet through to the mapping of the human genome and our understanding of the human brain, the more we understand, the more there seems to be for us to explore.
The aim of scientific thought, then, is to apply past experience to new circumstances; the instrument is an observed uniformity in the course of events. By the use of this instrument it gives us information transcending our experience, it enables us to infer things that we have not seen from things that we have seen; and the evidence for the truth of that information depends on our supposing that the uniformity holds good beyond our experience.
The use of solar energy has not been opened up because the oil industry does not own the sun.
Farming is the riskiest profession in the world since the fate of the crop is closely linked to the behaviour of the monsoon.
[T]here are depths of thousands of miles which are hidden from our inquiry. The only tidings we have from those unfathomable regions are by means of volcanoes, those burning mountains that seem to discharge their materials from the lowest abysses of the earth.
I am not accustomed to saying anything with certainty after only one or two observations.
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